The PEVK Region of Titin: Deciphering the Molecular Interactions of Elasticity

Abstract

Titin is an elastic protein which spans half a sarcomere in muscles. Active muscles contract using the movement of thin and thick filaments in a well established way, but not all types of contractions can be explained with existing models. Titin is known to play a role in certain types of contractions but this role is not well understood. There is a variety of titin isoforms, but there are two conserved types of domains in all isoforms: immunoglobulin repeats and the PEVK region. Previous studies have shown that titin elongates first by separating immunoglobulin domains followed by stretching of the PEVK region (which requires higher forces). The PEVK is a highly elastic region of titin with two different sequence patterns; lysine rich PPAK (positively charged) and glutamic acid rich poly-E (negatively charged). The goal of this project is to characterize the molecular interactions within the PEVK region, using human titin as a model, since these interactions towards titin's elasticity have not been clearly elucidated. Our initial work has been to characterize the interactions between single PPAK and poly-E sequences. Preliminary circular dichroism data of the PPAK and poly-E show a random coil structure, consistant with the literature. Circular dichroism spectra for PPAK and poly-E mixtures deviates from the additive spectra of the individual peptides under physiological ionic strengths, suggesting an interaction between PPAK and poly-E. We are now expanding these studies to include more complex sequences that contain varying number of PPAK and poly-E segments in the same peptide and using these constructs quantitate the interactions. These studies will help us to understand the molecular nature of PEVK region and the forces contributing for its elasticity.