Sudarshi Premawardhana Dassanayake Mudiyanselage, Zhang Fang, Xu Jin, Gage Matthew J
Chemistry Department, University of Massachusetts Lowell, Lowell, MA, 01854, USA.
UMass Movement Center, University of Massachusetts Lowell, Lowell, MA, 01854, USA.
Biochem Biophys Rep. 2020 Nov 21;24:100859. doi: 10.1016/j.bbrep.2020.100859. eCollection 2020 Dec.
The muscle protein titin plays a crucial role in passive elasticity and the disordered PEVK region within titin is central to that function. The PEVK region is so named due to its high proline, glutamate, valine and lysine content and the high charge density in this region results in a lack of organized structure within this domain. The PEVK region is highly extensible but the molecular interactions that contribute to the elastic nature of the PEVK still remain poorly described. The PEVK region is formed by two unique sequence motifs. The PPAK motif is a 26 to 28 amino acid sequence that contains a mixture of charged and hydrophobic residues and is the primary building block for the PEVK region. Poly-E sequence motifs vary in length and contain clusters of 3-4 glutamic acids distributed throughout the motif. In this study, we derived two 28-residue peptides from the human titin protein sequence and measured their structural characteristics over a range of pHs. Our results demonstrate that the poly-E peptide undergoes a shift from a more rigid and elongated state to a more collapsed state as pH decreases with the midpoint of this transition being at pH ~5.5. Interestingly, a similar conformational shift is not observed in the PPAK peptide. These results suggest that the poly-E motif might provide a nucleating site for the PEVK when the muscle is not in an extended state.
肌肉蛋白肌联蛋白在被动弹性中起着关键作用，肌联蛋白内无序的PEVK区域对该功能至关重要。PEVK区域因其高脯氨酸、谷氨酸、缬氨酸和赖氨酸含量而得名，该区域的高电荷密度导致该结构域内缺乏有组织的结构。PEVK区域具有高度可扩展性，但对其弹性本质起作用的分子相互作用仍描述甚少。PEVK区域由两个独特的序列基序形成。PPAK基序是一个26至28个氨基酸的序列，包含带电荷和疏水残基的混合物，是PEVK区域的主要构建单元。聚E序列基序长度各异，包含分布在整个基序中的3 - 4个谷氨酸簇。在本研究中，我们从人肌联蛋白序列中获得了两个28个残基的肽，并在一系列pH值下测量了它们的结构特征。我们的结果表明，随着pH值降低，聚E肽从更刚性和伸长的状态转变为更塌陷的状态，这种转变的中点在pH约5.5处。有趣的是，在PPAK肽中未观察到类似的构象转变。这些结果表明，当肌肉不处于伸展状态时，聚E基序可能为PEVK提供一个成核位点。
