title: Refolding of amphioxus insulin-like peptide: implications of a bifurcating evolution of the different folding behavior of insulin and insulin-like growth factor 1.
abstract: Insulin and insulin-like growth factor 1 (IGF-1) share high sequence homology, but their folding behaviors are significantly different: insulin folds into one unique thermodynamically controlled structure, while IGF-1 folds into two thermodynamically controlled disulfide isomers. However, the origin of their different folding behaviors is still elusive. The amphioxus insulin-like peptide (ILP) is thought to be the common ancestor of insulin and IGF-1. A recombinant single-chain ILP has been expressed previously, and now its folding behavior is investigated. The folding behavior of ILP shows the characteristics of both insulin and IGF-1. On one hand, two thermodynamically controlled disulfide isomers of ILP have been identified; on the other hand, the content of isomer 1 (its disulfides are deduced identical to those of swap IGF-1) is much less than that of isomer 2 (its disulfides are deduced identical to those of native IGF-1); that is, more than 96% of ILP folds into the native structure. The present results suggest that the different folding behaviors of insulin and IGF-1 are acquired through a bifurcating evolution: the tendency of forming the thermodynamically controlled non-native disulfide isomer is diminished during evolution from ILP to insulin, while this tendency is amplified during evolution from ILP to IGF-1. Moreover, the N-terminal Gln residue of ILP can spontaneously form a pyroglutamate residue, and its cyclization has a significant effect on the folding behavior of ILP: the percentage of isomer 1 is approximately 2-fold that of isomer 1 of the noncyclized ILP; that is, isomer 1 becomes more favored when the N-terminal residue of ILP is cyclized. So, we deduce that the N-terminal residues have a significant effect on the folding properties of insulin, IGF-1, and ILP.
authors.affiliation: Life Science College, Jilin University, Changchun 130061, China.
authors.forename: Shuai
authors.initials: S
authors.lastname: Wang
authors.forename: Zhan-Yun
authors.initials: ZY
authors.lastname: Guo
authors.forename: Lu
authors.initials: L
authors.lastname: Shen
authors.forename: Ying-Jiu
authors.initials: YJ
authors.lastname: Zhang
authors.forename: You-Min
authors.initials: YM
authors.lastname: Feng
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D002942:Circular Dichroism; D004220:Disulfides / Q000737:chemistry; D019143:Evolution, Molecular; D007328:Insulin / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000235:genetics; D007334:Insulin-Like Growth Factor I / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry; D010449:Peptide Mapping; D017510:Protein Folding; D020033:Protein Isoforms / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics; D012697:Serine Endopeptidases / Q000378:metabolism
chemical_list: D004220:Disulfides; D007328:Insulin; D010446:Peptide Fragments; D020033:Protein Isoforms; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; C093255:amphioxus insulin-like peptide; D007334:Insulin-Like Growth Factor I; D012697:Serine Endopeptidases