Evolution and structural analysis of interleukin-17 / 第二军医大学学报

ABSTRACT

Objective To investigate the origin and protein structures of vertebrate interleukin-17 (IL-17) genes via phylogenetic and bioinformatic approaches. Methods All the known IL-17 protein sequences of human, zebrafish and amphioxus were retrieved from the National Center for Biotechnology Information (NCBI) and Joint Genome Institute (JGI) databases. Also, partial IL-17 sequences from seven other model organisms were collected from several specific databases. MEGA software package was used to reconstruct a phylogenetic tree for these sequences and MODELLER software was used to predict IL-17 three-dimensional models of zebrafish, amphioxus, ciona and caenorhabditis, and these models were then compared with the known crystal structure of human IL-17F. Results Although all the IL-17 protein sequences contained four conservative cysteine residues that may be involved in the formation of a typical cysteine knot, amphioxus IL-17 revealed two different distribution patterns, with one similar to that of vertebrates and one unique to amphioxus. Phylogenetic analysis and cysteine analysis showed that amphioxus genome had no ortholog of vertebrate IL-17 genes, but urochordate ciona genome had it. The structural comparison result of our three-dimensional models supported the phylogenetic tree. Conclusion Amphioxus IL-17 might be the divergent point in the IL-17 evolution. The ortholog of vertebrate IL-17 genes might first appear in urochordates.