Function-dependent clustering of orthologues and paralogues of cyclophilins

The 18 kDa archetypal cyclosporin-A binding protein, cyclophilin-A, has multiple paralogues in the human genome. Only 18 of those paralogues have been detected as mRNAs or proteins whose masses vary from 18 to 354 kDa, whereas the functional significance of the open reading frames (ORFs) encoding other paralogues of cyclophilin-A remains unknown. The genomes of Drosophila melanogaster, Caenorhabditis elegans, Arabidopsis thaliana, Schizosaccharomyces pombe, and Saccharomyces cerevisiae encode different numbers of the cyclophilin paralogues, some of which are orthologous to the human cyclophilins. A library of novel algorithms was developed and used for computation of the conservation levels for hydrophobicity and bulkiness profiles, and amino acid compositions (AACs) of 303 aligned sequences of cyclophilins. The majority of the paralogues and orthologues encoded in these 6 genomes differ considerably from each other. Some of the orthologues and paralogues have high correlation coefficients (CCFs) for pairwise compared hydrophobicity and bulkiness profiles, and whose AACs differ to a low degree. Convergence of these three properties of the polypeptide chain and apparent conservation of the typical sequence hallmarks and parameters allowed for the clustering of the functionally related orthologues and paralogues of the cyclophilins. The clustering method allowed for sorting out the cyclophilins into several distinct classes. Analyses of the overlapping clusters of sequences permitted delineation of some hypothetical pathways that might have led to the creation of certain paralogues of cyclophilins in the eukaryotic genomes. (C) 2004 Wiley-Liss, Inc.