| Type: | Family | Name: | Bombyxin |
| Description: | The insulin family of proteins groups together several evolutionarily related active peptides []: these include insulin [, ], relaxin [, ], insect prothoracicotropic hormone (bombyxin) [], insulin-like growth factors (IGF1 and IGF2) [, ], mammalian Leydig cell-specific insulin-like peptide (gene INSL3), early placenta insulin-like peptide (ELIP) (gene INSL4), locust insulin-related peptide (LIRP), molluscan insulin-related peptides (MIP), and Caenorhabditis elegans insulin-like peptides. The 3D structures of a number of family members have been determined [, , ]. The fold comprises two polypeptide chains (A and B) linked by two disulphide bonds: all share a conserved arrangement of 4 cysteines in their A chain, the first of which is linked by a disulphide bond to the third, while the second and fourth are linked by interchain disulphide bonds to cysteines in the B chain. This group represents bombyxins. Bombyxin is a brain peptide responsible for activation of prothoracic glands to produce ecdysone in insects []. When cleaved, bombyxins produce both subunits of the biologically active heterodimer. Several molecular species of bombyxin have now been identified in Bombyx, Agrius and Samia moth species. Both bombyxin and insulin contain six cysteine residues with identical distributions and are predicted to have similar tertiary structures, especially in their core regions []. They are not functionally equivalent however. The similarity to insulin has prompted speculation that it may play a role in the regulation of growth, and it has been shown to act as a growth factor for wing imaginal disks and midgut stem cells in some lepidopteran species [, ]. | Short Name: | Bombyxin |
