Cyclophilins and Their Functions in Abiotic Stress and Plant–Microbe Interactions

Plants have developed a variety of mechanisms and regulatory pathways to change their gene expression profiles in response to abiotic stress conditions and plant–microbe interactions. The plant–microbe interaction can be pathogenic or beneficial. Stress conditions, both abiotic and pathogenic, negatively affect the growth, development, yield and quality of plants, which is very important for crops. In contrast, the plant–microbe interaction could be growth-promoting. One of the proteins involved in plant response to stress conditions and plant–microbe interactions is cyclophilin. Cyclophilins (CyPs), together with FK506-binding proteins (FKBPs) and parvulins, belong to a big family of proteins with peptidyl-prolyl cis-trans isomerase activity (Enzyme Commission (EC) number 5.2.1.8). Genes coding for proteins with the CyP domain are widely expressed in all organisms examined, including bacteria, fungi, animals, and plants. Their different forms can be found in the cytoplasm, endoplasmic reticulum, nucleus, chloroplast, mitochondrion and in the phloem space. They are involved in numerous processes, such as protein folding, cellular signaling, mRNA processing, protein degradation and apoptosis. In the past few years, many new functions, and molecular mechanisms for cyclophilins have been discovered. In this review, we aim to summarize recent advances in cyclophilin research to improve our understanding of their biological functions in plant defense and symbiotic plant–microbe interactions.

Peptidyl-prolyl cis/trans isomerases in GtoPdb v.2021.2

Peptidyl-prolyl cis/trans isomerases (PPIases) are an enzyme family which catalyse the cis/trans isomerisation of proline peptide bonds to promote the folding and re-folding of peptides and proteins. Three subfamilies have been identified: cyclophilins, FK506-binding proteins and parvulins. Individual PPIases are overexpressed in a number of cancers [59], and family members have been targetted for immunosuppressant effects.

Two functionally redundant FK506-binding proteins regulate multidrug resistance gene expression and govern azole antifungal resistance

Increasing resistance to antifungal therapy is an impediment to effective treatment of fungal infections. Candida glabrata is an opportunistic human fungal pathogen which is inherently less susceptible to cost-effective azole antifungals. Gain-of-function mutations in the Zn-finger pleiotropic drug resistance transcriptional activator-encoding gene, CgPDR1, are the most prevalent cause of azole resistance in clinical settings. CgPDR1 is also transcriptionally activated upon azole exposure, however, factors governing CgPDR1 gene expression are not yet fully understood. Here, we have uncovered a novel role for two FK506-binding proteins, CgFpr3 and CgFpr4, in regulation of the CgPDR1 regulon. We show that CgFpr3 and CgFpr4 possess peptidyl-prolyl isomerase domain, and act redundantly to control CgPDR1 expression, as Cgfpr3Δ4Δ mutant displayed elevated expression of CgPDR1 gene, along with overexpression of its target genes, CgCDR1, CgCDR2 and CgSNQ2, that code for ATP-binding cassette multidrug transporters. Further, CgFpr3 and CgFpr4 are required for maintenance of histone H3 and H4 protein levels, and fluconazole exposure leads to elevated H3 and H4 protein levels. Consistent with a role of histone proteins in azole resistance, disruption of genes coding for the histone demethylase CgRph1 and histone H3K36-specific methyltransferase CgSet2 leads to increased and decreased susceptibility to fluconazole, respectively, with Cgrph1Δ mutant displaying significantly lower basal expression of CgPDR1 and CgCDR1 genes. These data underscore a hitherto unknown role of histone methylation in modulating the most common azole antifungal resistance mechanism. Altogether, our findings establish a link between CgFpr-mediated histone homeostasis and CgPDR1 gene expression, and implicate CgFpr in virulence of C. glabrata.

FKBP25 Regulates Meiotic Apparatus During Mouse Oocyte Maturation

FK506 binding proteins 25 (FKBP25) has been shown to function in ribosome biogenesis, chromatin organization, and microtubule stability in mitosis. However, the role of FKBP25 in oocyte maturation has not been investigated. Here, we report that oocytes with FKBP25 depletion display abnormal spindle assembly and chromosomes alignment, with defective kinetochore-microtubule attachment. Consistent with this finding, aneuploidy incidence is also elevated in oocytes depleted of FKBP25. Importantly, FKBP25 protein level in old oocytes is significantly reduced, and ectopic expression of FKBP25 could partly rescue the aging-associated meiotic defects. In addition, by employing site-specific mutagenesis, we identify that serine 163 is a major, if not unique, phosphorylation site modulating the action of FKBP25 on meiotic maturation. In summary, our data indicate that FKBP25 is a pivotal factor for determining oocyte quality, and may mediate the effects of maternal aging on female reproduction.

Designing Selective and Non-Immunosuppressive Antifungal FK506 Analogs: Structures, Biophysics and Dynamics of Fungal and Human Calcineurin-Inhibitor Complexes

Calcineurin is an attractive antifungal target due to its central role in fungal pathogenesis. The development of specific antifungals targeting calcineurin is complex, as calcineurin inhibitors, such as FK506, are immunosuppressive. Using fungal calcineurin-inhibitor crystal structures we recently developed a less immunosuppressive FK506 analog, APX879, with broad-spectrum antifungal activity and efficacy in a murine model of invasive fungal infection. To better understand the interaction of the human and fungal FK506-binding proteins (FKBP12) required for calcineurin inhibition at a molecular level, and guide the design of fungal-selective and non-immunosuppressive FK506 analogs, here we report the high-resolution structures of the M. circinelloides FKBP12 bound to FK506 and the human, A. fumigatus and M. circinelloides FKBP12 proteins bound to the FK506 analog, APX879. Combining structural, genetic and biophysical methodologies with molecular dynamics simulations, we identify critical variations in these structurally similar FKBP12:ligand complexes to enhance fungal-selectivity.