Characterization of beta-connectin (titin 2) from striated muscle by dynamic light scattering

Abstract

Connectin (titin) is a large filamentous protein (single peptide) with a molecular mass of approximately 3 MDa, contour length approximately 900 nm, and diameter approximately 4 nm, and resides in striated muscle. Connectin links the thick filaments to the Z-lines in a sarcomere and produces a passive elastic force when muscle fiber is stretched. The aim of this study is to elucidate some aspects of physical properties of isolated beta-connectin (titin 2), a proteolytic fragment of connectin, by means of dynamic light-scattering (DLS) spectroscopy. The analysis of DLS spectra for beta-connectin gave the translational diffusion coefficient of 3.60 x 10(-8) cm2/s at 10 degrees C (or the hydrodynamic radius of 44.1 nm), molecular mass little smaller than 3.0 MDa (for a literature value of sedimentation coefficient), the root-mean-square end-to-end distance of 163 nm (or the radius of gyration of 66.6 nm), and the Kuhn segment number of 30 and segment length of 30 nm (or the persistence length of 15 nm). These results permitted to estimate the flexural rigidity of 6.0 x 10(-20) dyn x cm2 for filament bending, and the elastic constant of 7 dyn/cm for extension of one persistence length. Based on a simple model, implications of the present results in muscle physiology are discussed.

Regulation of Muscle Tone & Tension

“…• This appearance is consistent with the normal compact conformation of the isolated protein that results from the inherent flexibility of the molecule, which derives from the flexible connections between its ~300 domains (Trinick et al 1984;Higuchi et al 1993). Molecules attached to mica and subjected to the 'combing' force (~800 pN) of the receding meniscus during drying showed a straightened and extended conformation (Fig.…”

Is titin a ‘winding filament’? A new twist on muscle contraction

“…The model is based on a sarcomere structure similar to rabbit psoas muscle [14,60], with a thin filament diameter of 10 nm [61] and a titin filament diameter of 4 nm [23,62]. The length of the PEVK segment is approximately 104 nm at SL ¼ 2.6 mm [14].…”

Low-force transitions in single titin molecules reflect a memory of contractile history

“…The lack of precise knowledge about the physiologically relevant force range to which a single titin molecule is exposed makes it difficult to pinpoint the potential mechanosensory mechanisms. It is hypothesized that the force per titin molecule in the physiological length range of sarcomeres is small (,0-20 pN) (Anderson and Granzier, 2012;Herzog et al, 2012;Higuchi et al, 1993;Linke and Leake, 2004;Linke et al, 1998a;Liversage et al, 2001). In this force regime, titin is thought to behave as a purely entropic chain devoid of internal interactions.…”