Variations of Sequences and Amino Acid Compositions of Proteins That Sustain Their Biological Functions: An Analysis of the Cyclophilin Family of Proteins

The sequences of the ubiquitous and phylogenetically diversified cyclophilin family of proteins were divided into six groups, namely, vertebrates, invertebrates, other metazoa, plants, fungi, and prokaryotes. These groups of sequences were aligned with the multiple sequence alignment program Clustal-W. The variations of amino acid substitutions and amino acid compositions for these six groups of cyclophilins were calculated using a novel suite of multiple-sequence alignment analysis routines. The cyclophilins from vertebrates can be divided for at least two distinct structural classes that differ from each other by a variable-length amino acid insert within the loop that links α-helix II and β-strand III. A similar structural feature is also present in the other groups of cyclophilins, namely, those from invertebrates, other metazoa, plants, and fungi. The sequences of cyclophilins from fungi and prokaryotes are more diversified than those from vertebrates, and their alterations involve structures other than the amino acid inserts within the loops. Variations of the hydrophobicity and bulkiness of amino acid substitutions of the aligned sequences were calculated for each group of cyclophilins and for the alignment of all the sequences. The variations have clear asymmetry that may signify the need for modification of the physical properties of certain fragments of cyclophilins that are involved in interactions with various cellular components in the evolving environment.