BBA - General Subjects (v.1850, #10)
Editorial Board (i).
Special Issue on Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets by Franz Schmid (1963-1964).
Real-time protein NMR spectroscopy and investigation of assisted protein folding by Amit Kumar; Jochen Balbach (1965-1972).
During protein-folding reactions toward the native structure, short-lived intermediate states can be populated. Such intermediates expose hydrophobic patches and can self-associate leading to non-productive protein misfolding. A major focus of current research is the characterization of short-lived intermediates and how molecular chaperones enable productive folding. Real-time NMR spectroscopy, together with the development of advanced methods, is reviewed here and the potential these methods have to characterize intermediate states as well as interactions with molecular chaperone proteins at single-residue resolution is highlighted.Various chaperone interactions can guide the protein-folding reaction and thus are important for protein structure formation, stability, and activity of their substrates. Chaperone-assisted protein folding, characterization of intermediates, and their molecular interactions using real-time NMR spectroscopy will be discussed. Additionally, recent advances in NMR methods employed for characterization of high-energy intermediates will be discussed.Real-time NMR combines high resolution with kinetic information of protein reactions, which can be employed not only for protein-folding studies and the characterization of folding intermediates but also to investigate the molecular mechanisms of assisted protein folding.Real-time NMR spectroscopy remains an effective tool to reveal structural details about the interaction between chaperones and transient intermediates. Methodologically, it provides in-depth understanding of how kinetic intermediates and their thermodynamics contribute to the protein-folding reaction. This review summarizes the most recent advances in this field. This article is part of a Special Issue titled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: Real-time NMR; Protein folding; Kinetic intermediates; Molecular chaperones;
Control of protein function by prolyl isomerization by Philipp A.M. Schmidpeter; Johanna R. Koch; Franz X. Schmid (1973-1982).
Background: Prolyl cis/trans isomerizations have long been known as critical and rate-limiting steps in protein folding.Results: Now it is clear that they are also used as slow conformational switches and molecular timers in the regulation of protein activity. Here we describe several such proline switches and how they are regulated.Conclusions and general significance: Prolyl isomerizations can function as attenuators and provide allosteric systems with a molecular memory. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: Protein folding; Protein regulation; Prolyl isomerase; Allostery; Signaling;
Ziploc-ing the structure: Triple helix formation is coordinated by rough endoplasmic reticulum resident PPIases by Yoshihiro Ishikawa; Sergei Boudko; Hans Peter Bächinger (1983-1993).
Protein folding is crucial for proteins' specific functions and is facilitated by various types of enzymes and molecular chaperones. The peptidyl prolyl cis/trans isomerases (PPIase) are one of these families of enzymes. They ubiquitously exist inside the cell and there are eight PPIases in the rough endoplasmic reticulum (rER), a compartment where the folding of most secreted proteins occurs.We review the functional and structural aspects of individual rER resident PPIases. Furthermore, we specifically discuss the role of these PPIases during collagen biosynthesis, since collagen is the most abundant protein in humans, is synthesized in the rER, and contains a proportionally high number of proline residues.The rER resident PPIases recognize different sets of substrates and facilitate their folding. Although they are clearly catalysts for protein folding, they also have more broad and multifaceted functions. We propose that PPIases coordinate collagen biosynthesis in the rER.This review expands our understanding of collagen biosynthesis by explaining the influence of novel indirect mechanisms of regulating folding and this is also explored for PPIases. We also suggest future directions of research to obtain a better understanding of collagen biosynthesis and functions of PPIases in the rER. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: Peptidyl prolyl cis/trans isomerase; Rough endoplasmic reticulum; Collagen; Molecular chaperone; Protein folding; Protein–protein interaction;
Computational perspective and evaluation of plausible catalytic mechanisms of peptidyl-prolyl cis–trans isomerases by Safieh Tork Ladani; Michael G. Souffrant; Arghya Barman; Donald Hamelberg (1994-2004).
Peptidyl prolyl cis–trans isomerization of the protein backbone is involved in the regulation of many biological processes. Cis–trans isomerization is notoriously slow and is catalyzed by a family of cis–trans peptidyl prolyl isomerases (PPIases) that have been implicated in many diseases. A general consensus on how these enzymes speed up prolyl isomerization has not been reached after decades of both experimental and computational studies.Computational studies carried out to understand the catalytic mechanism of the prototypical FK506 binding protein 12, Cyclophilin A and peptidyl-prolyl cis–trans isomerase NIMA-interacting 1 (Pin1) are reviewed. A summary and an evaluation of the implications of the proposed mechanisms from computational studies are presented.The analysis of computational studies and evaluation of the proposed mechanisms provide a general consensus and a better understanding of PPIase catalysis. The speedup of the rate of peptidyl-prolyl isomerization by PPIases can be best described by a catalytic mechanism in which the substrate in transition state configuration is stabilized. The enzymes preferentially bind the transition state configuration of the substrate relative to the cis conformation, which in most cases is bound better than the trans conformation of the substrate. Stabilization of the transition state configuration of the substrate leads to a lower free energy barrier and a faster rate of isomerization when compared to the uncatalyzed isomerization reaction.Fully understanding the catalytic mechanism of PPIases has broad implications for drug design, elucidation of the molecular basis of many diseases, protein engineering, and enzyme catalysis in general. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.Display Omitted
Keywords: Peptidyl-prolyl cis–trans isomerases; Cyclophilin A; FKPB; Pin1; Transition state stabilization; Substrate-destabilization;
Multidomain Peptidyl Prolyl cis/trans Isomerases by Cordelia Schiene-Fischer (2005-2016).
Peptidyl prolyl cis/trans isomerases (PPIases) assist the folding and restructuring of client proteins by catalysis of the slow rotational motion of peptide bonds preceding a proline residue. Catalysis is performed by relatively small, distinct protein domains of 10 to 18 kDa for all PPIase families. PPIases are involved in a wide variety of physiological and pathophysiological processes like signal transduction, cell differentiation, apoptosis as well as viral, bacterial and parasitic infection.There are multidomain PPIases consisting of one to up to four catalytic domains of the respective PPIase family supplemented by N- or C-terminal extensions. This review examines the biochemical and functional properties of the members of the PPIase class of enzymes which contain additional protein domains with defined biochemical functions.The versatile domain architecture of multidomain PPIases is important for the control of enzyme specificity and organelle-specific targeting, the establishment of molecular connections and hence the coordination of PPIase functions across the cellular network.Accessory domains covalently linked to a PPIase domain supply an additional layer of control to the catalysis of prolyl isomerization in specific client proteins. Understanding these control mechanisms will provide new insights into the physiological mode of action of the multidomain PPIases and their ability to form therapeutic targets. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: Peptidyl prolyl cis/trans isomerase; Multidomain; Cyclophilin; FKBP; Pin1;
Prolyl isomerases in gene transcription by Steven D. Hanes (2017-2034).
Peptidyl-prolyl isomerases (PPIases) are enzymes that assist in the folding of newly-synthesized proteins and regulate the stability, localization, and activity of mature proteins. They do so by catalyzing reversible (cis-trans) rotation about the peptide bond that precedes proline, inducing conformational changes in target proteins.This review will discuss how PPIases regulate gene transcription by controlling the activity of (1) DNA-binding transcription regulatory proteins, (2) RNA polymerase II, and (3) chromatin and histone modifying enzymes.Members of each family of PPIase (cyclophilins, FKBPs, and parvulins) regulate gene transcription at multiple levels. In all but a few cases, the exact mechanisms remain elusive. Structure studies, development of specific inhibitors, and new methodologies for studying cis/trans isomerization in vivo represent some of the challenges in this new frontier that merges two important fields.Prolyl isomerases have been found to play key regulatory roles in all phases of the transcription process. Moreover, PPIases control upstream signaling pathways that regulate gene-specific transcription during development, hormone response and environmental stress. Although transcription is often rate-limiting in the production of enzymes and structural proteins, post-transcriptional modifications are also critical, and PPIases play key roles here as well (see other reviews in this issue). This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.Display Omitted
Keywords: Immunophilins; Transcription regulation; RNA polymerase II CTD; Histone modification; Ess1; Pin1;
FKBPs and their role in neuronal signaling by Felix Hausch (2035-2040).
Ligands for FK506-binding proteins, also referred to as neuroimmunophilin ligands, have repeatedly been described as neuritotrophic, neuroprotective or neuroregenerative agents. However, the precise molecular mechanism of action underlying the observed effects has remained elusive, which eventually led to a reduced interest in FKBP ligand development.A survey is presented on the pharmacology of neuroimmunophilin ligands, of the current understanding of individual FKBP homologs in neuronal processes and an assessment of their potential as drug targets for CNS disorders.FKBP51 is the major target accounting for the neuritotrophic effect of neuroimmunophilin ligands. Selectivity against the homolog FKBP52 is essential for optimal neuritotrophic efficacy.Selectivity within the FKBP family, in particular selective inhibition of FKBP12 or FKBP51, is possible. FKBP51 is a pharmacologically tractable target for stress-related disorders. The role of FKBPs in neurodegeneration remains to be clarified. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.Display Omitted
Keywords: Neuroimmunophilin; FKBP51; FK506; Neurite outgrowth; Stress-related disorders;
Structural mechanisms of cyclophilin D-dependent control of the mitochondrial permeability transition pore by Manuel Gutiérrez-Aguilar; Christopher P. Baines (2041-2047).
Opening of the mitochondrial permeability transition pore is the underlying cause of cellular dysfunction during diverse pathological situations. Although this bioenergetic entity has been studied extensively, its molecular componentry is constantly debated. Cyclophilin D is the only universally accepted modulator of this channel and its selective ligands have been proposed as therapeutic agents with the potential to regulate pore opening during disease.This review aims to recapitulate known molecular determinants necessary for Cyclophilin D activity regulation and binding to proposed pore constituents thereby regulating the mitochondrial permeability transition pore.While the main target of Cyclophilin D is still a matter of further research, permeability transition is finely regulated by post-translational modifications of this isomerase and its catalytic activity facilitates pore opening.Complete elucidation of the molecular determinants required for Cyclophilin D-mediated control of the mitochondrial permeability transition pore will allow the rational design of therapies aiming to control disease phenotypes associated with the occurrence of this unselective channel. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: Mitochondrial permeability transition; Cyclophilin-D; Peptidyl-prolyl cis-trans isomerase;
Interaction of p53 with prolyl isomerases: Healthy and unhealthy relationships by Fiamma Mantovani; Alessandro Zannini; Alessandra Rustighi; Giannino Del Sal (2048-2060).
The p53 protein family, comprising p53, p63 and p73, is primarily involved in preserving genome integrity and preventing tumor onset, and also affects a range of physiological processes. Signal-dependent modifications of its members and of other pathway components provide cells with a sophisticated code to transduce a variety of stress signaling into appropriate responses. TP53 mutations are highly frequent in cancer and lead to the expression of mutant p53 proteins that are endowed with oncogenic activities and sensitive to stress signaling.p53 family proteins have unique structural and functional plasticity, and here we discuss the relevance of prolyl-isomerization to actively shape these features.The anti-proliferative functions of the p53 family are carefully activated upon severe stress and this involves the interaction with prolyl-isomerases. In particular, stress-induced stabilization of p53, activation of its transcriptional control over arrest- and cell death-related target genes and of its mitochondrial apoptotic function, as well as certain p63 and p73 functions, all require phosphorylation of specific S/T-P motifs and their subsequent isomerization by the prolyl-isomerase Pin1. While these functions of p53 counteract tumorigenesis, under some circumstances their activation by prolyl-isomerases may have negative repercussions (e.g. tissue damage induced by anticancer therapies and ischemia-reperfusion, neurodegeneration). Moreover, elevated Pin1 levels in tumor cells may transduce deregulated phosphorylation signaling into activation of mutant p53 oncogenic functions.The complex repertoire of biological outcomes induced by p53 finds mechanistic explanations, at least in part, in the association between prolyl-isomerases and the p53 pathway. This article is part of a Special Issue entitled Proline-directed foldases: Cell signaling catalysts and drug targets.Display Omitted
Keywords: Peptidyl-prolyl cis/trans isomerases; Pin1; p53; Apoptosis; Neurodegenerative diseases; Cancer;
Pleiotropic roles in cancer biology for multifaceted proteins FKBPs by Simona Romano; Anna D’Angelillo; Maria Fiammetta Romano (2061-2068).
FK506 binding proteins (FKBP) are multifunctional proteins highly conserved across the species and abundantly expressed in the cell. In addition to a well-established role in immunosuppression, FKBPs modulate several signal transduction pathways in the cell, due to their isomerase activity and the capability to interact with other proteins, inducing changes in conformation and function of protein partners. Increasing literature data support the concept that FKBPs control cancer related pathways.The aim of the present article is to review current knowledge on FKBPs roles in regulation of key signaling pathways associated with cancer.Some family members appear to promote disease while others are protective against tumorigenesis.FKBPs family proteins are expected to provide new biomarkers and small molecular targets, in the near future, increasing diagnostic and therapeutic opportunities in the cancer field. This article is part of a Special Issue entitled Proline-Directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: FK506 binding protein; Peptidyl-prolyl-isomerase; Tumorigenesis; Cancer;
Pin1 dysregulation helps to explain the inverse association between cancer and Alzheimer's disease by Jane A. Driver; Xiao Zhen Zhou; Kun Ping Lu (2069-2076).
Pin1 is an intracellular signaling molecule which plays a critical but opposite role in the pathogenesis of Alzheimer's disease (AD) and many human cancers.We review the structure and function of the Pin1 enzyme, the diverse roles it plays in cycling cells and neurons, the epidemiologic evidence for the inverse association between cancer and AD, and the potential therapeutic implications of Pin1-based therapies.Pin1 is a unique enzyme that has effects on the function of target proteins by “twisting” them into different shapes. Cycling cells use Pin1 to help coordinate cell division. It is over-expressed and/or activated by multiple mechanisms in many common human cancers, and acts on multiple signal pathways to promote tumorigenesis. Inhibition of Pin1 in animal models has profound anti-tumor effects. In contrast, Pin1 is down-regulated or inactivated by multiple mechanisms in AD brains. The absence of Pin1 impairs tau function and amyloid precursor protein processing, leading to tangle- and amyloid-related pathologies and neurodegeneration in an age-dependent manner, resembling human AD. We have developed cis and trans conformation-specific antibodies to provide the first direct evidence that tau exists in distinct cis and trans conformations and that Pin1 accelerates its cis to trans conversion, thereby protecting against tangle formation in AD.Available studies on Pin1 suggest that cancer and AD may share biological pathways that are deregulated in different directions. Pin1 biology opens exciting preventive and therapeutic horizons for both cancer and neurodegeneration. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: Pin1; Phosphorylation signaling; Cancer; Alzheimer's disease;
Pin1: Intimate involvement with the regulatory protein kinase networks in the global phosphorylation landscape by David W. Litchfield; Brian H. Shilton; Christopher J. Brandl; Laszlo Gyenis (2077-2086).
Protein phosphorylation is a universal regulatory mechanism that involves an extensive network of protein kinases. The discovery of the phosphorylation-dependent peptidyl-prolyl isomerase Pin1 added an additional layer of complexity to these regulatory networks.We have evaluated interactions between Pin1 and the regulatory kinome and proline-dependent phosphoproteome taking into consideration findings from targeted studies as well as data that has emerged from systematic phosphoproteomic workflows and from curated protein interaction databases.The relationship between Pin1 and the regulatory protein kinase networks is not restricted simply to the recognition of proteins that are substrates for proline-directed kinases. In this respect, Pin1 itself is phosphorylated in cells by protein kinases that modulate its functional properties. Furthermore, the phosphorylation-dependent targets of Pin1 include a number of protein kinases as well as other enzymes such as phosphatases and regulatory subunits of kinases that modulate the actions of protein kinases.As a result of its interactions with numerous protein kinases and their substrates, as well as itself being a target for phosphorylation, Pin1 has an intricate relationship with the regulatory protein kinase and phosphoproteomic networks that orchestrate complex cellular processes and respond to environmental cues.This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.Display Omitted
Keywords: Protein kinase; Kinome; Phosphoproteome; Proline-directed kinase; Pin1; Peptidyl–prolyl isomerase;
Extracellular cyclophilins in health and disease by Michael Bukrinsky (2087-2095).
Extracellular cyclophilins (eCyPs) are pro-inflammatory factors implicated in pathogenesis of a number of inflammatory diseases. Most pathogenic activities of eCyPs are related to their chemotactic action towards leukocytes, which is mediated by eCyP receptor on target cells, CD147, and involves peptidyl–prolyl cis–trans isomerase activity of cyclophilins. This activity is inhibited by cyclosporine A (CsA) and non-immunosuppressive derivatives of this drug. Accumulating evidence for the role of eCyPs in disease pathogenesis stimulated research on the mechanisms of eCyP-initiated events, resulting in identification of multiple signaling pathways, characterization of a variety of effector molecules released from eCyP-treated cells, and synthesis of CsA derivatives specifically blocking eCyPs. However, a number of important questions related to the mode of action of eCyPs remain unanswered.In this article, we integrate available information on release and function of extracellular cyclophilins into a unified model, focusing on outstanding issues that need to be clarified.Extracellular cyclophilins are critical players in pathogenesis of a number of inflammatory diseases. Their mechanism of action involves interaction with the receptor, CD147, and initiation of a poorly characterized signal transduction process culminating in chemotaxis and production of pro-inflammatory factors.Extracellular cyclophilins present an attractive target for therapeutic interventions that can be used to alleviate symptoms and consequences of acute and chronic inflammation. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: CD147; Extracellular cyclophilin; Cyclosporine A; Disease model; Chemotaxis; Inflammation;
FKBPs in bacterial infections by Can M. Ünal; Michael Steinert (2096-2102).
FK506-binding proteins (FKBPs) contain a domain with peptidyl–prolyl-cis/trans-isomerase (PPIase) activity and bind the immunosuppressive drugs FK506 and rapamycin. FKBPs belong to the immunophilin family and are found in eukaryotes and bacteria.In this review we describe two major groups of bacterial virulence-associated FKBPs, the trigger factor and Mip-like PPIases. Moreover, we discuss the contribution of host FKBPs in bacterial infection processes.Since PPIases are regarded as alternative antiinfective drug targets we highlight current research strategies utilizing pipecolinic acid and cycloheximide derivatives as well as substrate based inhibitors.The current research strategies suggest a beneficial synergism of drug development and basic research.This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: FK506-binding protein; Macrophage infectivity potentiator (Mip); Bacteria; Pathogen; Infection; Drug target;
The role of immunophilins in viral infection by Sam Hopkins; Philippe A. Gallay (2103-2110).
Tremendous progress has been made in the past 20 years in understanding the roles played by immunophilins, and in particular the cyclophilins, in supporting the replication cycles of human viruses. A growing body of genetic and biochemical evidence and data from clinical trials confirm that cyclophilins are essential cofactors that contribute to establishing a permissive environment within the host cell that supports the replication of HIV-1 and HCV. Cyclophilin A regulates HIV-1 replication kinetics and infectivity, modulates sensitivity to host restriction factors, and cooperates in the transit of the pre-integration complex into the nucleus of infected cells. Cyclophilin A is an essential cofactor whose expression supports HCV-specific RNA replication in human hepatocytes.Peptidyl-prolyl isomerase inhibitors have been used in clinical trials to validate cyclophilins as antiviral targets for the treatment of HIV-1 and Chronic Hepatitis C virus infection and as molecular probes to identify the roles played by immunophilins in supporting the replication cycles of human viruses.This review summarizes emerging research that defines the functions of immunophilins in supporting the replication cycles of HIV-1, HCV, HBV, coronaviruses, and other viral pathogens and describes new information that suggests a role for immunophilins in regulating innate immune responses against chronic viral infection.The dependence on cyclophilins by evolutionarily distinct viruses for accomplishing various steps in replication such as viral entry, initiation of genomic nucleic acid replication, viral genome uncoating, nuclear import and nuclear entry, emphasizes the potential of cyclophilin inhibitors as therapeutic agents. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: Immunophilins; Cyclophilins; Viruses; HIV-1; HCV; Cyclophilin inhibitors;
Biosynthesis of cyclosporins and other natural peptidyl prolyl cis/trans isomerase inhibitors by Alfons Lawen (2111-2120).
Peptidyl-prolyl-cis/trans-isomerases (PPIases) are ubiquitously expressed and have been implicated in a wide range of biological functions. Their inhibition is beneficial in immunosuppression, cancer treatment, treatment of autoimmune diseases, protozoan and viral infections.Three classes of PPIases are known, each class having their own specific inhibitors. This review will cover the present knowledge on the biosynthesis of the natural PPIase inhibitors. These include for the cyclophilins: the cyclosporins, the analogues of peptolide SDZ 214-103 and the sanglifehrins; for the FKBPs: ascomycin, rapamycin and FK506 and for the parvulins the naphtoquinone juglone.Over the last thirty years much progress has been made in understanding PPIase function and the biosynthesis of natural PPIase inhibitors. Non-immunosuppressive analogues were discovered and served as lead compounds for the development of novel antiviral drugs. There are, however, still unsolved questions which deserve further research into this exciting field.As all the major natural inhibitors of the cyclophilins and FKBPs are synthesized by complex non-ribosomal peptide synthetases and/or polyketide synthases, total chemical synthesis is not a viable option. Thus, fully understanding the modular enzyme systems involved in their biosynthesis may help engineering enzymes capable of synthesizing novel PPIase inhibitors with improved functions for a wide range of conditions. This article is part of a Special Issue entitled Proline-directed Foldases: Cell signaling catalysts and drug targets.
Keywords: Cyclosporin analogues; Cyclosporin synthetase; SDZ 214-103; Sanglifehrins; Rapamycin and analoges; Juglone;
Semi-synthesis of cyclosporins by Michael Peel; Andrew Scribner (2121-2144).
Since its isolation in 1970, and discovery of its potent inhibitory activity on T-cell proliferation, cyclosporin A (CsA) has been shown to play a significant role in diverse fields of biology. Furthermore, chemical modification of CsA has led to analogs with distinct biological activities associated with its protein receptor family, cyclophilins.This review systematically collates the synthetic chemistry performed at each of the eleven amino acids, and provides examples of the utility of such transformations. The various modifications of CsA are traced from early, modest chemistry performed at the unique Bmt residue, through the remarkable use of a polyanion enolate that can be stereoselectively manipulated, and onto application of more recently developed olefin metathesis chemistry to prepare new CsA derivatives with unexpected biological activity.The myriad biological activities of CsA and its synthetic derivatives have inspired the development of new approaches to modify the CsA ring. In turn, these new CsA derivatives have served as tools in the discovery of new roles for cyclophilins.This review provides information on the types of cyclosporin derivatives that are available to the many biologists working in this field, and should be of value to the medicinal chemist trying to discover drugs based on CsA. This article is part of a Special Issue entitled Proline-directed foldases: Cell signaling catalysts and drug targets.
Keywords: Cyclosporine; Cyclophilin; Semi-synthesis; Cyclic peptide;
Plant immunophilins: a review of their structure-function relationship by Dileep Vasudevan; Gayathri Gopalan; Ashish Kumar; Veder J. Garcia; Sheng Luan; Kunchithapadam Swaminathan (2145-2158).
Originally discovered as receptors for immunosuppressive drugs, immunophilins consist of two major groups, FK506 binding proteins (FKBPs) and cyclosporin A binding proteins (cyclophilins, CYPs). Many members in both FKBP and CYP families are peptidyl prolyl isomerases that are involved in protein folding processes, though they share little sequence homology. It is not surprising to find immunophilins in all organisms examined so far, including viruses, bacteria, fungi, plants and animals, as protein folding represents a common process in all living systems.Studies on plant immunophilins have revealed new functions beyond protein folding and new structural properties beyond that of typical PPIases. This review focuses on the structural and functional diversity of plant FKBPs and CYPs.The differences in sequence, structure as well as subcellular localization, have added on to the diversity of this family of molecular chaperones. In particular, the large number of immunophilins present in the thylakoid lumen of the photosynthetic organelle, promises to deliver insights into the regulation of photosynthesis, a unique feature of plant systems. However, very little structural information and functional data are available for plant immunophilins.Studies on the structure and function of plant immunophilins are important in understanding their role in plant biology. By reviewing the structural and functional properties of some immunophilins that represent the emerging area of research in plant biology, we hope to increase the interest of researchers in pursuing further research in this area.This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.
Keywords: Immunophilin; FK506; FKBP; Cyclophilin; Cyclosporin; Redox;