03/10/2021
By Matthew Gage

The Kennedy College of Science, Department of Chemistry, invites you to attend a doctoral dissertation defense by Sudarshi Premawardhana entitled “The Sensitivity of Poly-E Motifs in the PEVK Region of Titin to the Calcium and pH Fluctuations.” The defense will be held on March 22 at noon via Zoom. Please contact Matthew Gage for meeting information if you are interested in attending.

The committee will be composed of Matthew Gage (chair), Jin Xu, Jeffery Moore and Nicolai Konow. A brief abstract is provided below.

Abstract: The PEVK region of the giant protein titin is a disordered region contributing to the passive elasticity in muscle. This region is enriched in the amino acids proline, glutamate, valine and lysine. The PEVK region contains two sequence motifs, PPAK and poly-E, due to the sequence composition of these motifs. PEVK region is believed to act as an entropically driven spring but there is evidence supporting an enthalpic contribution as well due to the observed lower stiffness of PEVK at decreased ionic strength. The poly-E regions in PEVK have high densities of negative charge from the clusters of 3-4 glutamates and thus are presumably more sensitive to the ionic and pH fluctuations in muscle than PPAK motifs. Poly-E regions have exhibited reduced bending rigidity in the presence of calcium levels and extended conformations at higher pH, both further suggesting an enthalpic contribution to PEVK elasticity. In this work, we studied the pH dependency of both peptides derived from the PPAK and poly-E motifs and longer PEVK constructs containing multiple PPAK and poly-E motifs. We also studied the ionic strength (Ca2+, Mg2+, K+ and Na+) dependency of these longer proteins as well. In both systems, the poly-E motif constructs exhibited pH dependent conformational changes and in the studies on the longer PEVK constructs conformational shifts were also observed in the presence of both K+ and Na+. Interestingly, the conformational changes in the poly-E motif are different in the presence of the PPAK motif, suggesting the presence of interactions between the two motifs, which have been elusive to observe in other studies. While the poly-E exhibits very dynamic behavior in response to its environment, the PPAK protein did not exhibit any pH or calcium dependent conformational shifts. Taken together, these results suggest that the structure of poly-E motifs is sensitive to pH and calcium and the presence of PPAK motifs alters the degree of such structural and functional responses of poly-E.

All interested students and faculty members are invited to attend.