Sequences of B-chain/domain 1-10/1-9 of insulin and insulin-like growth factor 1 determine their different folding behavior.
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.
Chen
Yan
Y
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.
You
You
Y
Jin
Rui
R
Guo
Zhan-Yun
ZY
Feng
You-Min
YM
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
D004220:Disulfides; D007328:Insulin; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D007334:Insulin-Like Growth Factor I