The human FK506-binding proteins: characterization of human FKBP19.

Analysis of the human repertoire of the FK506-binding protein (FKBP) family of peptidyl-prolyl cis/trans isomerases has identified an expansion of genes that code for human FKBPs in the secretory pathway. There are distinct differences in tissue distribution and expression levels of each variant. In this article we describe the characterization of human FKBP19 (Entrez Gene ID: FKBP11), an FK506-binding protein predominantly expressed in vertebrate secretory tissues. The FKBP19 sequence comprises a cleavable N-terminal signal sequence followed by a putative peptidyl-prolyl cis/trans isomerase domain with homology to FKBP12. This domain binds FK506 weakly in vitro. FKBP19 mRNA is abundant in human pancreas and other secretory tissues and high levels of FKBP19 protein are detected in the acinar cells of mouse pancreas.

The cyclophilin repertoire of the fission yeast Schizosaccharomyces pombe.

The cyclophilin repertoire of the fission yeast Schizosaccharomyces pombe is comprised of nine members that are distributed over all three of its chromosomes and range from small single-domain to large multi-domain proteins. Each cyclophilin possesses only a single prolyl-isomerase domain, and these vary in their degree of consensus, including at positions that are likely to affect their drug-binding ability and catalytic activity. The additional identified motifs are involved in putative protein or RNA interactions, while a novel domain that is specific to SpCyp7 and its orthologues may have functions that include an interaction with hnRNPs. The Sz. pombe cyclophilins are found throughout the cell but appear to be absent from the mitochondria, which is unique among the characterized eukaryotic repertoires. SpCyp5, SpCyp6 and SpCyp8 have exhibited significant upregulation of their expression during the meiotic cycle and SpCyp5 has exhibited significant upregulation of its expression during heat stress. All nine have identified members in the repertoires of H. sapiens, D. melanogaster and A. thaliana. However, only three identified members in the cyclophilin repertoire of S. cerevisiae with SpCyp7 identifying a fourth protein that is not a member of the recognized repertoire due to its possession of a degenerate prolyl-isomerase domain. The cyclophilin repertoire of Sz. pombe therefore represents a better model group for the study of cyclophilin function in the higher eukaryotes.

Identification and comparative analysis of the peptidyl-prolyl cis/trans isomerase repertoires of H. sapiens, D. melanogaster, C. elegans, S. cerevisiae and Sz. pombe.

The peptidyl-prolyl cis/trans isomerase (PPIase) class of proteins comprises three member families that are found throughout nature and are present in all the major compartments of the cell. Their numbers appear to be linked to the number of genes in their respective genomes, although we have found the human repertoire to be smaller than expected due to a reduced cyclophilin repertoire. We show here that whilst the members of the cyclophilin family (which are predominantly found in the nucleus and cytoplasm) and the parvulin family (which are predominantly nuclear) are largely conserved between different repertoires, the FKBPs (which are predominantly found in the cytoplasm and endoplasmic reticulum) are not. It therefore appears that the cyclophilins and parvulins have evolved to perform conserved functions, while the FKBPs have evolved to fill ever-changing niches within the constantly evolving organisms. Many orthologous subgroups within the different PPIase families appear to have evolved from a distinct common ancestor, whereas others, such as the mitochondrial cyclophilins, appear to have evolved independently of one another. We have also identified a novel parvulin within Drosophila melanogaster that is unique to the fruit fly, indicating a recent evolutionary emergence. Interestingly, the fission yeast repertoire, which contains no unique cyclophilins and parvulins, shares no PPIases solely with the budding yeast but it does share a majority with the higher eukaryotes in this study, unlike the budding yeast. It therefore appears that, in comparison with Schizosaccharomyces pombe, Saccharomyces cerevisiae is a poor representation of the higher eukaryotes for the study of PPIases.

Shortfalls in the peptidyl-prolyl cis-trans isomerase protein Pin1 in neurons are associated with frontotemporal dementias.

The peptidyl-prolyl cis-trans isomerase (PPIase) Pin1 modulates the activity of a range of target proteins involved in the cell cycle, transcription, translation, endocytosis, and apoptosis by facilitating dephosphorylation of phosphorylated serine or threonine residue preceding a proline (p-Ser/Thr-Pro) motifs catalyzed by phosphatases specific for the trans conformations. Pin1 targets include the neuronal microtubule-associated protein tau, whose dephosphorylation restores its ability to stabilize microtubules. We, and others, have shown that tau hyperphosphorylation in the neurofibrillary tangles (NFTs) of Alzheimer disease (AD) is associated with redirection of the predominantly nuclear Pin1 to the cytoplasm and with Pin1 shortfalls throughout subcellular compartments. As nuclear Pin1 depletion causes apoptosis, shortfalls in regard to both nuclear and p-tau targets may contribute to neuronal dysfunction. We report here that similar Pin1 redistribution and shortfalls occur in frontotemporal dementias (FTDs) characterized by abnormal protein aggregates of tau and other cytoskeletal proteins. This may be a unifying, contributory factor towards neuronal death in these dementias.

Cyclophilin sensitivity to sanglifehrin A can be correlated to the same specific tryptophan residue as cyclosporin A.

Sanglifehrin A (SFA) is a recently discovered immunosuppressant drug that shares its intracellular target with the major immunosuppressant drug cyclosporin A (CsA). Both bind to and inhibit the cyclophilins, a diverse family of proteins found throughout nature that share a conserved catalytic domain. Although they share this common protein target, the mechanism of action of the cyclophilin-SFA complex has been reported as distinct from that of the well-studied cyclophilin-CsA complex. The X-ray structure of a macrolide analogue of SFA's cyclic region complexed with cyclophilin A has recently been resolved, but this left the placement of the linear region of SFA unresolved. Using five cyclophilins from the fission yeast Schizosaccharomyces pombe, and a mutant of one of these proteins, SpCyp3-F128W, we have shown that the sensitivity of cyclophilins to SFA can be correlated to the same specific tryptophan residue that has previously been identified to correlate to CsA sensitivity, and that the tail of SFA may be responsible for mediating this sensitivity.

Identification and characterisation of Schizosaccharomyces pombe cyclophilin 3, a cyclosporin A insensitive orthologue of human USA-CyP.

We have identified nine cyclophilins encoded in the genome of the fission yeast Schizosaccharomyces pombe (Sp). Cyclophilin 3 is an orthologue of hUSA-CyP, which is associated with Prp4/Prp3 in the [U4/U6.U5] snRNP complex and Prp18, both of which are components of the pre-mRNA splicing machinery. PPIase assays have shown SpCyp3 and hUSA-CyP to have comparable activity and substrate specificity, but SpCyp3 has a reduced sensitivity to CsA correlating with a difference in the catalytic site. Prp3, Prp4 and Prp18 proteins exist in S. pombe and nuclear localisation of SpCyp3 has been shown, indicating conservation of function between hUSA-CyP and SpCyp3.