Study Of The Giant Muscle Protein Pevk-rich Domain Of The Structure And Function

Titin represents a family of giant elastic proteins mainly in skeletal and cardiac muscles, which was found and reported by Marugama and Wang in 1970s. Its multifaceted functions include the assembly of the muscle sarcomere, the maintenance of sarcomere symmetry and integrity and the generation of passive tension. In the I-band region, where titin extends during passive force development, there is a unique PEVK motif that consists of 70% of proline, glutamate, valine, and lysine residues. So, it is very important to study the exact nature of both the structure and elasticity of the PEVK segment.In the study, tetrapeptide EVPK in PEVK segment of titin was synthesized through Fmoc solid phase peptide synthesis. Its molecular weight was determined by ESI-MS and its sequence and structure were determined by MS/MS and 2D-NMR . The proline residue are trans-proline residues, mainly. Its conformational analysis by the molecular modeling methods shows that the folded conformations are the preferred backbone conformations. When resting muscle is stretched, the unfolding of the molecule may result in the extension of it and accompany the rise in passive tension moderately. And the results are consistant with the former exprimental results and the quantum calculational ones.The eonformational analyses of PP Ⅱ motifs PVAP, PKKP and PEVP were carried out with stochastic search, simulated annealing and hybrid Monte Carlo. The sampled multiple conformations of the there PP Ⅱ motifs tell us that all the three peptide backbones were divided into two groups: the folded conformation and the extended conformation, and the the folded conformations have the lowest energy. Under strech, the folded-to-extended interconversion can lead to the elasticity of the peptides. The flexibility of PPII helices may have important functional roles in the PEVK segment of titin, which is involved in sarcomere assembly and muscle elasticity.The Ramachandran plots of the 28-residue PEVK module for human foetal titin (PR) and its three subfragments (PR1,PR2, PR3) indicate the tendency of the presence of PPII helices. So. they may be the flexible spacer regions of titin.