Unravelling the complexity of silk sericins:P150/sericin 6is a new silk gene inBombyx mori

Abstract

ABSTRACTSericins are a small family of highly divergent proteins that serve as adhesives and coatings for silk fibers and are produced in the middle part of the silk gland. So far, five genes encoding sericin proteins have been found inBombyx mori. Sericins 1 and 3 are responsible for silk adhesion in the cocoon, while sericins 2, 4, and 5 are present in non-cocoon spun silk of younger larvae (including the early last instar). We found a new gene, which we namedP150/sericin 6, which appears to be an ortholog of the sericin-like protein previously found inGalleria mellonella. TheB. morisequence of theP150/sericin 6ORF was previously incorrectly predicted and assigned to two smaller, uncharacterized genes. We present a newP150/sericin 6gene model and show that it encodes a large protein of 467 kDa. It is characterized by repeats with a high proportion of threonine residues and a short conserved region with a cysteine knot motif (CXCXCX) at the C-terminus. Expression analysis has shown thatB. mori P150/ser6has low transcriptional level in contrast to itsG. mellonellahomolog. We also discuss the synteny of homologous genes on corresponding chromosomes between moth species and possible phylogenetic relationships betweenP150/ser6and cysteine knot mucins. Our results improve our understanding of the evolutionary relationships between adhesion proteins in different lepidopteran species.