MOLECULAR BASIS OF TITIN ELASTICITY

描述（改编自摘要）：被动弹性特性在肌肉生理学中起着关键作用。它们决定了心跳时心室的充盈量和翅膀扇动时储存的机械能量。肌粘连蛋白是一种杆状的模块化蛋白质，在肌节的M线和Z线之间延伸。肌球蛋白与肌节I带重叠的区域负责肌节的被动弹性特性。然而，允许titin在力作用下延伸的分子机制尚不清楚。I波段titin由免疫球蛋白（Ig）样结构域的串联重复序列和富含氨基酸、P、E、V和K的多肽区（PEVK区）组成。有人提出，I带titin的弹性性质是由其单个模块的展开/再折叠反应和PEVK区域的弹性决定的。本提案的主要目的是结合生物物理和分子生物学技术来研究人类心肌I带titin弹性的分子基础。为了实现这一目标，研究人员将利用最近开发的原子力显微镜（AFM）技术，该技术能够测量单个蛋白质的机械特性。他们将使用AFM来测量单个I带titin模块的机械稳定性和动力学，并将使用这些模块的工程串联重复序列的诱变来检查展开和再折叠的决定因素。串联模块化蛋白质将由模块的混合物组成，以检查由不同机械稳定性和动力学的机械单元组合而成的弹性。测量将检查构象的变化，使titin模块可逆地延伸下施加的力。他们的研究旨在阐明模块化弹性蛋白的机械结构以及Ig和FNIII模块可扩展性的分子基础。这些模块的机械特性也可能具有更广泛的意义，因为它们是大量其他蛋白质的典型构建块。

DESCRIPTION (Adapted from abstract): Passive elastic properties play a critical role in muscle physiology. They determine the filling volume of a ventricle during a heartbeat and the amount of mechanical energy stored during the flap of a wing. Titin is a rod-like modular protein that stretches between the M and Z lines of a sarcomere. The region of titin that overlaps with the sarcomeric I band is responsible for the passive elastic properties of the sarcomere. However, the molecular mechanisms that allow titin to extend under force are not known. I band titin is composed of tandem repeats of immunoglobulin (Ig) like domains and a polypeptide region rich in amino acids, P,E,V, and K (the PEVK region). It has been proposed that the elastic properties of I band titin result from the unfolding/refolding reactions of its individual modules and the elasticity of the PEVK region. The main objective of this proposal is to combine biophysical and molecular biological techniques to examine the molecular basis of the elasticity of the I band titin from human cardiac muscle. Towards this aim the investigators will exploit recently developed atomic force microscopy (AFM) techniques that are capable of measuring the mechanical properties of single proteins. They will use AFM to measure the mechanical stability and kinetics of individual I band titin modules, and will use mutagenesis of engineered tandem repeats of these modules to examine the determinants of unfolding and refolding. Tandem modular proteins will be engineered composed of mixtures of modules, to examine the elasticity that results from combining mechanical units of different mechanical stability and kinetics. The measurements will examine the conformational changes that allow titin modules to reversibly extend under an applied force. They studies are aimed at elucidating the mechanical architecture of a modular elastic protein and the molecular basis of the extensibility of Ig and FNIII modules. The mechanical properties of these modules may also find wider significance since they are typical building blocks of a large number of other proteins.