Journal
BIOCHEMICAL JOURNAL
Volume 374, Issue -, Pages 687-695Publisher
PORTLAND PRESS LTD
DOI: 10.1042/BJ20030702
Keywords
circular dichroism (CD); elastic protein; nuclear magnetic resonance (NMR); polyproline II helix-coil (PhC) motif; titin; trans-to-cis-proline isomerization
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To understand the structural basis of molecular elasticity and protein interaction of the elastic PEVK (Pro-Glu-Val-Lys) segment of the giant muscle protein titin, we carried out a detailed analysis of a representative PEVK module and a 16-module PEVK protein under various environmental conditions. Three conformational states, polyproline II (PPII) helix, beta-turn and unordered coil were identified by CID and NMR. These motifs interconvert without Iona-range co-operativity. As a general trend, the relative content of PPII increases with lower temperature and higher polarity, beta-turn increases with lower temperature and lower polarity, and unordered coil increases with higher temperature and higher polarity. NMR studies demonstrate that trans-proline residues are the predominant form at room temperature (22 degreesC), with little trans-to-cis isomerization below 35 degreesC. Ionic strength affects salt bridges between charged side chains, but not the backbone conformation. We conclude that titin PEVK conformation is malleable and responds to subtle environmental changes without cooperativity. This gradual conformational transition may represent a regulatory mechanism for fine-tuning protein interactions and elasticity.
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