title: Sequences of B-chain/domain 1-10/1-9 of insulin and insulin-like growth factor 1 determine their different folding behavior.
abstract: Although insulin and insulin-like growth factor-1 (IGF-1) belong to one family, insulin folds into one thermodynamically stable structure, while IGF-1-folds into two thermodynamically stable structures (native and swap forms). We have demonstrated previously that the bifurcating folding behavior of IGF-1 is mainly controlled by its B-domain. To further elucidate which parts of the sequences determine their different folding behavior, by exchanging the N-terminal sequences of mini-IGF-1 and recombinant porcine insulin precursor (PIP), we prepared four peptide models: [1-9]PIP, [1-10]mini-IGF-1, [1-4]PIP, and [1-5]mini-IGF-1 by means of protein engineering, and their disulfide rearrangement, V8 digestion, circular dichroic spectra, disulfide stability, and in vitro refolding were investigated. Among them only [1-9]PIP, like mini-IGF-1/IGF-1, was expressed in yeast as two isomers: isomer 1 (corresponding to swap IGF-1) and isomer 2 (corresponding to native IGF-1), which are supported by the experimental results of disulfide rearrangements, peptide mapping of V8 endoprotenase digests, circular dichroic analysis, in vitro refolding, and disulfide stability analysis. The other peptide models, [1-10]mini-IGF-1, [1-4]PIP, and [1-5]mini-IGF-1, fold into one stable structure as PIP does, which indicates that sequence 1-4 of mini-IGF-1 is important for the folding behavior of mini-IGF-1/IGF-1 but not sufficient to lead to a bifurcating folding. The results demonstrated that the folding information, by which mini-IGF-1/IGF-1-folds into two thermodynamically structures, is encoded/written in its sequence 1-9, while sequences 1-10 of B chain in insulin/PIP play an important role in the guide of its unique disulfide pairing during the folding process.
authors.affiliation: Key Laboratory of Proteomics, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences Graduate School, The Chinese Academy of Sciences, Shanghai 200031, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Chen
authors.forename: You
authors.initials: Y
authors.lastname: You
authors.forename: Rui
authors.initials: R
authors.lastname: Jin
authors.forename: Zhan-Yun
authors.initials: ZY
authors.lastname: Guo
authors.forename: You-Min
authors.initials: YM
authors.lastname: Feng
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D004220:Disulfides; D006801:Humans; D007328:Insulin / Q000737:chemistry*; D007334:Insulin-Like Growth Factor I / Q000737:chemistry*; D007536:Isomerism; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D015003:Yeasts / Q000235:genetics
chemical_list: D004220:Disulfides; D007328:Insulin; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D007334:Insulin-Like Growth Factor I