Evolution and structural analysis of interleukin-17

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.