Abstract
Abstract The hydrogen bonding, hydrophobic interactions, and the turn effect are three factors affecting the stability of □-structures. Generally, the □-turn is thought to play an important role in stabilizing the □-structures. Previous studies in our group have disclosed that replacing DPro with Asp destabilizes the peptide whose DPG segment is in type II’ turn. More specifically, the DP to D mutation at DP-6 position caused an one amino-acid frameshift of the first □-strand toward the turn region and resulted in side-chain inversion of the first □-strand to give a five-residue TSDGK turn which is composed of a type I turn plus a □ bulge. However, a similar mutation at the DP-14 position did not change the hydrogen bond network and formed a VDGO turn instead of the VDPGO turn. The VDGO turn is in type II’ turn. The frameshift in the first hairpin raises the questions: whether the structural rearrangement is driven by the new turn sequence or by the hydrophobic interactions of new strand pairings. Here, we have replaced the TSDGK turn with the VDGO turn in the first hairpin to examine the driving force. In this work, we used this small □-sheet to study the early stage of protein folding. This method is based on photolysis of caged □-sheet. The photolabile linker caged the □-sheet to alter its structure. When peptide is exposed to the 308- and 366- nm light, the linker can be cleaved rapidly. The refolding begins as soon as the photolabile linker is cleaved. We used the technique of Photoacoustic Calorimetry to study the refolding kinetics of the □-sheet.