Effects of Cofactors on Conformation Transition of Random Peptides Consisting of a Reduced Amino Acid Alphabet

This study aims to explore the structure characteristic of random polypeptides constructed by origin early amino acid alphabet, as well as the effects of cofactors on conformation transition of random peptides. DNA library R8-4 encoding VNM random peptides were constructed by small cassette strategy. Subsequently, a random polypeptide library was constructed using in vitro translation. Expression and purification of VNM random peptides were also performed by a conventional method of recombinant. CD spectrum analysis indicated that VNM random polypeptides have a secondary structure characteristic of protein, such as the content of α-helix is greater than 60%, random coil is about 20% β sheet, and β turn is less than 10%. CD spectrum changed with the addition of 10–40 µM ATP and NADP, but slightly changed by NAD; no influence was observed with MgSO4. Bis-ANS binding assay indicated that fluorescent intensity of bis-ANS was strengthened slightly by 10 µM random peptides. Fluorescent intensity was strengthened fourfold by adding 10–40 µM ATP, NAD, and NADH, whereas the inducing effect of NADPH and MgSO4 were negligible. VNM random peptides have a classic secondary structure and hydrophobic domain in water solution. Moreover, conformation transition and hydrophobic domain could be induced by cofactor, indicating the preliminary evidence for the hypothesis that “the origin of primitive protein was induced by small molecule.”