Reducing FKBP51 Expression in the Ventral Hippocampus Decreases Auditory Fear Conditioning in Male Rats.

Fear conditioning evokes a physiologic release of glucocorticoids that assists learning. As a cochaperone in the glucocorticoid receptor complex, FKBP51 modulates stress-induced glucocorticoid signaling and may influence conditioned fear responses. This study combines molecular and behavioral approaches to examine whether locally reducing FKBP51 expression in the ventral hippocampus is sufficient to affect fear-related behaviors. We hypothesized that reducing FKBP51 expression in the VH would increase glucocorticoid signaling to alter auditory fear conditioning. Adult male rats were injected with an adeno-associated virus (AAV) vector expressing short hairpin - RNAs (shRNA) targeting FKBP5 into the ventral hippocampus to reduce FKBP5 levels or a control AAV. Infusion of FKBP5-shRNA into the ventral hippocampus decreased auditory fear acquisition and recall. Although animals injected with FKBP5-shRNA showed less freezing during extinction recall, the difference was due to a reduced fear recall rather than improved extinction. Reducing ventral hippocampus FKBP51 did not affect exploratory behavior in either the open field test or the elevated zero maze test but did increase passive behavior in the forced swim test, suggesting that the reduction in auditory fear recall was not due to more active responses to acute stress. Furthermore, lower ventral hippocampus FKBP51 levels did not alter corticosterone release in response to restraint stress, suggesting that the reduced fear recall was not due to lower corticosterone release. Our findings suggest FKBP51 in the ventral hippocampus plays a selective role in modulating fear-learning processes and passive behavioral responses to acute stress rather than hypothalamic-pituitary-adrenal axis reactivity or exploratory responses.

The transportosome system as a model for the retrotransport of soluble proteins.

The classic model of action of the glucocorticoid receptor (GR) sustains that its associated heat-shock protein of 90-kDa (HSP90) favours the cytoplasmic retention of the unliganded GR, whereas the binding of steroid triggers the dissociation of HSP90 allowing the passive nuclear accumulation of GR. In recent years, it was described a molecular machinery called transportosome that is responsible for the active retrograde transport of GR. The transportosome heterocomplex includes a dimer of HSP90, the stabilizer co-chaperone p23, and FKBP52 (FK506-binding protein of 52-kDa), an immunophilin that binds dynein/dynactin motor proteins. The model shows that upon steroid binding, FKBP52 is recruited to the GR allowing its active retrograde transport on cytoskeletal tracks. Then, the entire GR heterocomplex translocates through the nuclear pore complex. The HSP90-based heterocomplex is released in the nucleoplasm followed by receptor dimerization. Subsequent findings demonstrated that the transportosome is also responsible for the retrotransport of other soluble proteins. Importantly, the disruption of this molecular oligomer leads to several diseases. In this article, we discuss the relevance of this transport machinery in health and disease.

Identification of FKBP10 prognostic value in lung adenocarcinoma patients with surgical resection of brain metastases: A retrospective single-institution cohort study.

OBJECTIVE: To explore the expression levels and clinical value of FKBP10 in lung adenocarcinoma brain metastases. DESIGN: A retrospective single-institution cohort study. PATIENTS: The perioperative records of 71 patients with lung adenocarcinoma brain metastases who underwent surgical resection at the authors' institution between November 2012 and June 2019 were retrospectively analyzed. METHODS: The authors evaluated FKBP10 expression levels using immunohistochemistry in tissue arrays of these patients. Kaplan-Meier survival curves were constructed, and a Cox proportional hazards regression model was used to identify independent prognostic biomarkers. A public database was used to detect FKBP10 expression and its clinical value in primary lung adenocarcinoma. RESULTS: The authors found that the FKBP10 protein was selectively expressed in lung adenocarcinoma brain metastases. Survival analysis showed that FKBP10 expression (p = 0.02, HR = 2.472, 95% CI [1.156, 5.289]), target therapy (p < 0.01, HR = 0.186, 95% CI [0.073, 0.477]), and radiotherapy (p = 0.006, HR = 0.330, 95% CI [0.149, 0.731]) were independent prognostic factors for survival in lung adenocarcinoma patients with brain metastases. The authors also detected FKBP10 expression in primary lung adenocarcinoma using a public database, found that FKBP10 is also selectively expressed in primary lung adenocarcinoma, and affects the overall survival and disease-free survival of patients. LIMITATIONS: The number of enrolled patients was relatively small and patients' treatment options varied. CONCLUSIONS: A combination of surgical resection, adjuvant radiotherapy, and precise target therapy may benefit the survival of selected patients with lung adenocarcinoma brain metastases. FKBP10 is a novel biomarker for lung adenocarcinoma brain metastases, which is closely associated with survival time and may serve as a potential therapeutic target.

SUMO regulation of FKBP51 activity and the stress response.

Glucocorticoids (GCs) actions are mostly mediated by the GC receptor (GR), a member of the nuclear receptor superfamily. Alterations of the GR activity have been associated to different diseases including mood disorders. FKBP51 is a GR chaperone that has gained much attention because it is a strong inhibitor of GR activity. FKBP51 exerts effects on many stress-related pathways and may be an important mediator of emotional behavior. Key proteins involved in the regulation of the stress response and antidepressant action are regulated by SUMOylation, a post-translational modification that has an important role in the regulation of neuronal physiology and disease. In this review, we focus on the role of SUMO-conjugation as a regulator of this pathway.

DNA methylation in regulatory elements of the FKBP5 and NR3C1 gene in mother-child binomials with depression.

BACKGROUND: The FKBP5 and NR3C1 genes play an important role in stress response, thus impacting mental health. Stress factor exposure in early life, such as maternal depression, may contribute to epigenetic modifications in stress response genes, increasing the susceptibility to different psychopathologies. The present study aimed to evaluate the DNA methylation profile in maternal-infant depression in regulatory regions of the FKBP5 gene and the alternative promoter of the NR3C1 gene. METHODS: We evaluated 60 mother-infant pairs. The levels of DNA methylation were analyzed by the MSRED-qPCR technique. RESULTS: We observed an increased DNA methylation profile in the NR3C1 gene promoter in children with depression and children exposed to maternal depression (p < 0.05). In addition, we observed a correlation of DNA methylation between mothers and offspring exposed to maternal depression. This correlation shows a possible intergenerational effect of maternal MDD exposure on the offspring. For FKBP5, we found a decrease in DNA methylation at intron 7 in children exposed to maternal MDD during pregnancy and a correlation of DNA methylation between mothers and children exposed to maternal MDD (p < 0.05). LIMITATIONS: Although the individuals of this study are a rare group, the sample size of the study was small, and we evaluated the DNA methylation of only one CpG site for each region. CONCLUSION: These results indicate changes in DNA methylation levels in regulatory regions of FKBP5 and NR3C1 in the mother-child MDD context and represent a potential target of studies to understand the depression etiology and how it occurs between generations.

Idiopathic subfertility in stallions. Clinical approaches to a complex problem

At least 30-40% of stallions in commercial breeding programs are moderately fertile and 8-12% are subfertile (0.5-3% with severe subfertility). From the total reported cases of the subfertility, in 2-20% of the stallions the cause is unknown or was not established. The objective of this work is to present the concept of subfertile stallion based on the current state of knowledge and advanced molecular diagnostic technologies. Low pregnancy rates have been reported in stallions with normal semen quality after conventional evaluation. Acrosome reaction (AR) is necessary for natural fertilization and impaired acrosome reaction (IAR) leads to subfertility or infertility in horses, however, AR test is not included in routine semen analysis. Genome-wide association study identified FKBP6 as a strong candidate gene responsible for this failure. The gene encodes for FK506 binding protein 6 (FKBP6) which is involved in sperm development and functions. We could conclude that the evaluation of the acrosomal status is essential in cases of stallions with good motility, concentration, morphology and viability but unexplained (idiopathic) subfertility or infertility. It is important to highlight the recent increase in reports of fertility problems in stallions related to disorders of genetic origin.(AU)

Identification of FKBP10 prognostic value in lung adenocarcinoma patients with surgical resection of brain metastases: A retrospective single-institution cohort study

Abstract Objective To explore the expression levels and clinical value of FKBP10 in lung adenocarcinoma brain metastases. Design A retrospective single-institution cohort study. Patients The perioperative records of 71 patients with lung adenocarcinoma brain metastases who underwent surgical resection at the authors' institution between November 2012 and June 2019 were retrospectively analyzed. Methods The authors evaluated FKBP10 expression levels using immunohistochemistry in tissue arrays of these patients. Kaplan-Meier survival curves were constructed, and a Cox proportional hazards regression model was used to identify independent prognostic biomarkers. A public database was used to detect FKBP10 expression and its clinical value in primary lung adenocarcinoma. Results The authors found that the FKBP10 protein was selectively expressed in lung adenocarcinoma brain metastases. Survival analysis showed that FKBP10 expression (p = 0.02, HR = 2.472, 95% CI [1.156, 5.289]), target therapy (p < 0.01, HR = 0.186, 95% CI [0.073, 0.477]), and radiotherapy (p = 0.006, HR = 0.330, 95% CI [0.149, 0.731]) were independent prognostic factors for survival in lung adenocarcinoma patients with brain metastases. The authors also detected FKBP10 expression in primary lung adenocarcinoma using a public database, found that FKBP10 is also selectively expressed in primary lung adenocarcinoma, and affects the overall survival and disease-free survival of patients. Limitations The number of enrolled patients was relatively small and patients' treatment options varied. Conclusions A combination of surgical resection, adjuvant radiotherapy, and precise target therapy may benefit the survival of selected patients with lung adenocarcinoma brain metastases. FKBP10 is a novel biomarker for lung adenocarcinoma brain metastases, which is closely associated with survival time and may serve as a potential therapeutic target.

FK506 binding protein 51: Its role in the adipose organ and beyond.

There is a great body of evidence that the adipose organ plays a central role in the control not only of energy balance, but importantly, in the maintenance of metabolic homeostasis. Interest in the study of different aspects of its physiology grew in the last decades due to the pandemic of obesity and the consequences of metabolic syndrome. It was not until recently that the first evidence for the role of the high molecular weight immunophilin FK506 binding protein (FKBP) 51 in the process of adipocyte differentiation have been described. Since then, many new facets have been discovered of this stress-responsive FKBP51 as a central node for precise coordination of many cell functions, as shown for nuclear steroid receptors, autophagy, signaling pathways as Akt, p38 MAPK, and GSK3, as well as for insulin signaling and the control of glucose homeostasis. Thus, the aim of this review is to integrate and discuss the recent advances in the understanding of the many roles of FKBP51 in the adipose organ.

The Scaffold Immunophilin FKBP51 Is a Phosphoprotein That Undergoes Dynamic Mitochondrial-Nuclear Shuttling.

The immunophilin FKBP51 forms heterocomplexes with molecular chaperones, protein-kinases, protein-phosphatases, autophagy-related factors, and transcription factors. Like most scaffold proteins, FKBP51 can use a simple tethering mechanism to favor the efficiency of interactions with partner molecules, but it can also exert more complex allosteric controls over client factors, the immunophilin itself being a putative regulation target. One of the simplest strategies for regulating pathways and subcellular localization of proteins is phosphorylation. In this study, it is shown that scaffold immunophilin FKBP51 is resolved by resolutive electrophoresis in various phosphorylated isoforms. This was evidenced by their reactivity with specific anti-phosphoamino acid antibodies and their fade-out by treatment with alkaline phosphatase. Interestingly, stress situations such as exposure to oxidants or in vivo fasting favors FKBP51 translocation from mitochondria to the nucleus. While fasting involves phosphothreonine residues, oxidative stress involves tyrosine residues. Molecular modeling predicts the existence of potential targets located at the FK1 domain of the immunophilin. Thus, oxidative stress favors FKBP51 dephosphorylation and protein degradation by the proteasome, whereas FK506 binding protects the persistence of the post-translational modification in tyrosine, leading to FKBP51 stability under oxidative conditions. Therefore, FKBP51 is revealed as a phosphoprotein that undergoes differential phosphorylations according to the stimulus.

Transcriptional epigenetic regulation of Fkbp1/Pax9 genes is associated with impaired sensitivity to platinum treatment in ovarian cancer.

BACKGROUND: In an effort to contribute to overcoming the platinum resistance exhibited by most solid tumors, we performed an array of epigenetic approaches, integrating next-generation methodologies and public clinical data to identify new potential epi-biomarkers in ovarian cancer, which is considered the most devastating of gynecological malignancies. METHODS: We cross-analyzed data from methylome assessments and restoration of gene expression through microarray expression in a panel of four paired cisplatin-sensitive/cisplatin-resistant ovarian cancer cell lines, along with publicly available clinical data from selected individuals representing the state of chemoresistance. We validated the methylation state and expression levels of candidate genes in each cellular phenotype through Sanger sequencing and reverse transcription polymerase chain reaction, respectively. We tested the biological role of selected targets using an ectopic expression plasmid assay in the sensitive/resistant tumor cell lines, assessing the cell viability in the transfected groups. Epigenetic features were also assessed in 189 primary samples obtained from ovarian tumors and controls. RESULTS: We identified PAX9 and FKBP1B as potential candidate genes, which exhibited epigenetic patterns of expression regulation in the experimental approach. Re-establishment of FKBP1B expression in the resistant OVCAR3 phenotype in which this gene is hypermethylated and inhibited allowed it to achieve a degree of platinum sensitivity similar to the sensitive phenotype. The evaluation of these genes at a translational level revealed that PAX9 hypermethylation leads to a poorer prognosis in terms of overall survival. We also set a precedent for establishing a common epigenetic signature in which the validation of a single candidate, MEST, proved the accuracy of our computational pipelines. CONCLUSIONS: Epigenetic regulation of PAX9 and FKBP1B genes shows that methylation in non-promoter areas has the potential to control gene expression and thus biological consequences, such as the loss of platinum sensitivity. At the translational level, PAX9 behaves as a predictor of chemotherapy response to platinum in patients with ovarian cancer. This study revealed the importance of the transcript-specific study of each gene under potential epigenetic regulation, which would favor the identification of new markers capable of predicting each patient's progression and therapeutic response.

Regulatory functions of FKBP5 intronic regions associated with psychiatric disorders.

The FKBP5 gene codifies a co-chaperone protein associated with the modulation of glucocorticoid receptor interaction involved in the adaptive stress response. The FKBP5 intracellular concentration affects the binding affinity of the glucocorticoid receptor (GR) to glucocorticoids (GCs). This gene has glucocorticoid response elements (GREs) located in introns 2, 5 and 7, which affect its expression. Recent studies have examined GRE activity and the effects of genetic variants on transcript efficiency and their contribution to susceptibility to behavioral disorders. Epigenetic changes and environmental factors can influence the effects of these allele-specific variants, impacting the response to GCs of the FKBP5 gene. The main epigenetic mark investigated in FKBP5 intronic regions is DNA methylation, however, few studies have been performed for all GREs located in these regions. One of the major findings was the association of low DNA methylation levels in the intron 7 of FKBP5 in patients with psychiatric disorders. To date, there are no reports of DNA methylation in introns 2 and 5 of the gene associated with diagnoses of psychiatric disorders. This review highlights what has been discovered so far about the relationship between polymorphisms and epigenetic targets in intragenic regions, and reveals the gaps that need to be explored, mainly concerning the role of DNA methylation in these regions and how it acts in psychiatric disease susceptibility.

Bioinformatic Analysis of Two TOR (Target of Rapamycin)-Like Proteins Encoded by Entamoeba histolytica Revealed Structural Similarities with Functional Homologs.

The target of rapamycin (TOR), also known as FKBP-rapamycin associated protein (FRAP), is a protein kinase belonging to the PIKK (phosphatidylinositol 3-kinase (PI3K)-related kinases) family. TOR kinases are involved in several signaling pathways that control cell growth and proliferation. Entamoeba histolytica, the protozoan parasite that causes human amoebiasis, contains two genes encoding TOR-like proteins: EhFRAP and EhTOR2. To assess their potential as drug targets to control the cell proliferation of E. histolytica, we studied the structural features of EhFRAP and EhTOR2 using a biocomputational approach. The overall results confirmed that both TOR amoebic homologs share structural similarities with functional TOR kinases, and show inherent abilities to form TORC complexes and participate in protein-protein interaction networks. To our knowledge, this study represents the first in silico characterization of the structure-function relationships of EhFRAP and EhTOR2.

Differential regulation of the glucocorticoid receptor nucleocytoplasmic shuttling by TPR-domain proteins.

A dimer of the heat-shock protein of 90-kDa (Hsp90) represents the critical core of the chaperone complex associated to the glucocorticoid receptor (GR) oligomer. The C-terminal end of the Hsp90 dimer shapes a functional acceptor site for co-chaperones carrying tetratricopeptide repeat (TPR) domains, where they bind in a mutually exclusive and competitive manner. They impact on the biological properties of the GR•Hsp90 complex and are major players of the GR transport machinery. Recently, we showed that the overexpression of a chimeric TPR peptide influences the subcellular distribution of GR. In this study, the functional role of endogenous proteins carrying TPR or TPR-like sequences on GR subcellular distribution was characterized. It is demonstrated that, contrarily to the positive influence of FKBP52 on GR nuclear accumulation, FKBP51 and 14-3-3 impaired this property. While SGT1α showed no significant effect, the overexpression of the Ser/Thr phosphatase PP5 resulted in a nearly equal nuclear-cytoplasmic redistribution of GR rather than its typical cytoplasmic localization in the absence of steroid. This observation led to analyse the influence of the phosphorylation status of GR, which resulted not linked to its nucleo-cytoplasmic shuttling mechanism. Nonetheless, it was evidenced that both PP5 and FKBP52 are related to the anchorage of the GR to nucleoskeleton structures. The influence of these TPR domain proteins on the steroid-dependent transcriptional activity of GR was also characterized. It is postulated that the pleiotropic actions of the GR in different cell types may be the consequence of the relative abundance of different TPR-domain interacting co-chaperones.

Role of Mitochondrial Heat-shock Proteins and Immunophilins in Neuro Degenerative Diseases.

Pathophysiologic conditions of neurodegenerative diseases are unquestionably related to protein misfolding. The accumulation of misfolded proteins into relatively ordered structures such as fibrillar intracellular and extracellular amyloids results in tissue lesions that lead to neuronal loss and brain damage. In these pathologies, the occurrence of protein aggregates suggests certain inefficient or insufficient cellular responses of those molecular chaperones that should properly assist the folding of the client proteins. In this regard, most experimental models for neurodegenerative diseases have demonstrated that the overexpression of molecular chaperones provides effective neuroprotection. A subset of these molecular chaperones corresponds to a group of proteins that exhibit peptidylprolyl isomerase enzymatic activity, the immunophilins. Most of the family members of the latter group were first described as being responsible for the immunosuppressive response or they were reported as members of the chaperone complex associated with HSP90 in steroid receptor oligomers. In this article, we review some aspects of the liaison between molecular chaperones and neurodegenerative diseases, in particular heat-shock proteins and immunophilins with demonstrated influence on the proper function of mitochondria. This article is intended to address a field that represents a yet critical unmet clinical need for the development of neuroprotective molecules focused on potentially novel molecular targets.

Moderate Aerobic Exercise Training Prevents the Augmented Hepatic Glucocorticoid Response Induced by High-Fat Diet in Mice.

Glucocorticoids (GCs) are critical regulators of energy balance. Their deregulation is associated with the development of obesity and metabolic syndrome. However, it is not understood if obesity alters the tissue glucocorticoid receptor (GR) response, and moreover whether a moderate aerobic exercise prevents the alteration in GR response induced by obesity. METHODS: To evaluate the GR response in obese mice, we fed C57BL6J mice with a high-fat diet (HFD) for 12 weeks. Before mice were sacrificed, we injected them with dexamethasone. To assess the exercise role in GR response, we fed mice an HFD and subjected them to moderate aerobic exercise three times a week. RESULTS: We found that mice fed a high-fat diet for 12 weeks developed hepatic GC hypersensitivity without changes in the gastrocnemius or epididymal fat GR response. Therefore, moderate aerobic exercise improved glucose tolerance, increased the corticosterone plasma levels, and prevented hepatic GR hypersensitivity with an increase in epididymal fat GR response. CONCLUSION: Collectively, our results suggest that mice with HFD-induced obesity develop hepatic GR sensitivity, which could enhance the metabolic effects of HFD in the liver. Moreover, exercise was found to be a feasible non-pharmacological strategy to prevent the deregulation of GR response in obesity.

Proof that the high molecular weight immunophilin FKBP52 mediates the in vivo neuroregenerative effect of the macrolide FK506.

The immunosuppressant drug FK506 (or tacrolimus) is a macrolide that binds selectively to immunophilins belonging to the FK506-binding protein (FKBP) subfamily, which are abundantly expressed proteins in neurons of the peripheral and central nervous systems. Interestingly, it has been reported that FK506 increases neurite outgrowth in cell cultures, implying a potential impact in putative treatments of neurodegenerative disorders and injuries of the nervous system. Nonetheless, the mechanism of action of this compound is poorly understood and remains to be elucidated, with the only certainty that its neurotrophic effect is independent of its primary immunosuppressant activity. In this study it is demonstrated that FK506 shows efficient neurotrophic action in vitro and profound effects on the recovery of locomotor activity, behavioural features, and erectile function of mice that underwent surgical spinal cord injury. The recovery of the locomotor activity was studied in knock-out mice for either immunophilin, FKBP51 or FKBP52. The experimental evidence demonstrates that the neurotrophic actions of FK506 are the consequence of its binding to FKBP52, whereas FK506 interaction with the close-related partner immunophilin FKBP51 antagonises the function of FKBP52. Importantly, our study also demonstrates that other immunophilins do not replace FKBP52. It is concluded that the final biological response is the resulting outcome of the drug binding to both immunophilins, FKBP51 and FKBP52, the latter being the one that commands the dominant neurotrophic action in vivo.

Regulation of the Ca2+-activated chloride channel Anoctamin-1 (TMEM16A) by Ca2+-induced interaction with FKBP12 and calcineurin.

Chloride fluxes through the calcium-gated chloride channel Anoctamin-1 (TMEM16A) control blood pressure, secretion of saliva, mucin, insulin, and melatonin, gastrointestinal motility, sperm capacitation and motility, and pain sensation. Calcium activates a myriad of regulatory proteins but how these proteins affect TMEM16A activity is unresolved. Here we show by co-immunoprecipitation that increasing intracellular calcium with ionomycin or by activating sphingosine-1-phosphate receptors, induces coupling of calcium/calmodulin-dependent phosphatase calcineurin and prolyl isomerase FK506-binding protein 12 (FKBP12) to TMEM16A in HEK-293 cells. Application of drugs that target either calcineurin (cyclosporine A) or FKBP12 (tacrolimus known as FK506 and sirolimus known as rapamycin) caused a decrease in TMEM16A activity. In addition, FK506 and BAPTA-AM prevented co-immunoprecipitation between FKBP12 and TMEM16A. FK506 rendered the channel insensitive to cyclosporine A without altering its apparent calcium sensitivity whereas zero intracellular calcium blocked the effect of FK506. Rapamycin decreased TMEM16A activity in cells pre-treated with cyclosporine A or FK506. These results suggest the formation of a TMEM16A-FKBP12-calcineurin complex that regulates channel function. We conclude that upon a cytosolic calcium increase the TMEM16A-FKPB12-calcineurin trimers are assembled. Such hetero-oligomerization enhances TMEM16A channel activity but is not mandatory for activation by calcium.

Nucleocytoplasmic shuttling of the glucocorticoid receptor is influenced by tetratricopeptide repeat-containing proteins.

It has been demonstrated that tetratricopeptide-repeat (TPR) domain proteins regulate the subcellular localization of glucocorticoid receptor (GR). This study analyses the influence of the TPR domain of high molecular weight immunophilins in the retrograde transport and nuclear retention of GR. Overexpression of the TPR peptide prevented efficient nuclear accumulation of the GR by disrupting the formation of complexes with the dynein-associated immunophilin FKBP52 (also known as FKBP4), the adaptor transporter importin-ß1 (KPNB1), the nuclear pore-associated glycoprotein Nup62 and nuclear matrix-associated structures. We also show that nuclear import of GR was impaired, whereas GR nuclear export was enhanced. Interestingly, the CRM1 (exportin-1) inhibitor leptomycin-B abolished the effects of TPR peptide overexpression, although the drug did not inhibit GR nuclear export itself. This indicates the existence of a TPR-domain-dependent mechanism for the export of nuclear proteins. The expression balance of those TPR domain proteins bound to the GR-Hsp90 complex may determine the subcellular localization and nucleocytoplasmic properties of the receptor, and thereby its pleiotropic biological properties in different tissues and cell types.

Backbone and side chain 1H, 15N and 13C assignments of a putative peptidyl prolyl cis-trans isomerase FKBP12 from Mycobacterium tuberculosis.

FK506 Binding Proteins (FKBPs) are a family of highly conserved and important proteins that possess a peptidyl cis-trans isomerase (PPIases) domain. Human FKBP12 is a prototype of this family and it is involved in many diseases due to its interaction with the immunosuppressive drugs FK506 and rapamycin. They inhibit calcineurin and mTOR complex, respectively, leading to parasite death by inhibiting cell proliferation through cytokinesis blockade being an important target to find new drugs. Tuberculosis is a disease that causes important impacts on public health worldwide. In this context, MtFKBP12 is a putative peptidyl prolyl cis-trans isomerase from Mycobacterium tuberculosis and here we report the NMR chemical shift assignment for 1H, 15N and 13C nuclei in the backbone and side chains of the MtFKBP12. This lays the foundation for further structural studies, backbone dynamics, mapping of interactions and drug screening and development. We have found through the NMR spectrum that the protein is well folded with narrow peaks and almost none overlap in 15N-HSQC. Prediction of secondary structure using Talos-N server showed great similarity with other proteins from this family.

Biological Actions of the Hsp90-binding Immunophilins FKBP51 and FKBP52

Immunophilins are a family of proteins whose signature domain is the peptidylprolyl-isomerase domain. High molecular weight immunophilins are characterized by the additional presence of tetratricopeptide-repeats (TPR) through which they bind to the 90-kDa heat-shock protein (Hsp90), and via this chaperone, immunophilins contribute to the regulation of the biological functions of several client-proteins. Among these Hsp90-binding immunophilins, there are two highly homologous members named FKBP51 and FKBP52 (FK506-binding protein of 51-kDa and 52-kDa, respectively) that were first characterized as components of the Hsp90-based heterocomplex associated to steroid receptors. Afterwards, they emerged as likely contributors to a variety of other hormone-dependent diseases, stress-related pathologies, psychiatric disorders, cancer, and other syndromes characterized by misfolded proteins. The differential biological actions of these immunophilins have been assigned to the structurally similar, but functionally divergent enzymatic domain. Nonetheless, they also require the complementary input of the TPR domain, most likely due to their dependence with the association to Hsp90 as a functional unit. FKBP51 and FKBP52 regulate a variety of biological processes such as steroid receptor action, transcriptional activity, protein conformation, protein trafficking, cell differentiation, apoptosis, cancer progression, telomerase activity, cytoskeleton architecture, etc. In this article we discuss the biology of these events and some mechanistic aspects.