Isomorphisms in tropomyosin modulate binding, flexibility and thin filament function

点击翻译按钮获取中文摘要

Living organisms move. The most spectacular examples are muscles that have a striped appearance under the microscope. We rely on them daily for blood circulation, posture, speed activates the motor myosin. The outcome is substantial ATP hydrolysis and contraction. When Ca(II) is taken back up, the reverse happens and relaxation ensues. Tropomyosin is able to do this because: (a) it polymerises with itself, forming a flexible, continuous strand and (b) its interactions with other proteins (eg actin, troponin) are Ca(II)-sensitive.******Part (I). 'Tuning' tropomyosin. The diversity of animal locomotion is an outcome of different types of muscle - fast, slow and cardiac - that deploy isoforms of the myofilament proteins to contract and relax. Protein isoforms are like cousins; they bear a family resemblance but have distinguishing features (eg slightly different amino acid sequences). How tropomyosin contributes to muscle diversity has long-been an enigma. ******The major isoforms of tropomyosin are Tpm1.1 (formerly ) ). They share 39 amino acid substitutions. The 'big' Q. What do they do differently? was answered only recently (Lohmeier-Vogel 50) not yet studied at the protein level.*********Part (II). Tropomyosin in extreme conditions The problem of cold for a protein is rigidity. During the winter, the N. Atlantic approaches freezing, a drop of > 30 oC compared to the warm-blooded (mammalian) scenario. Yet this is a natural marine habitat. A 'big' Q. is: How does tropomyosin avoid being straitjacketed'? Recent work (Fudge & Heeley 2015) has shown the existence of 3 'flexing' strategies (fewer ion pairs, more glycine & polar residues in core sites) within salmon Tpm1.1. The effect of these 'cold isomorphisms' on salmon Tpm1.1 function - polymerisation, troponin binding & regulation - will be probed by interchange of amino acids with the thermally-stable mammalian homologue. Part (II), as with Part (I), will provide information on tropomyosin's functional landscape (ie binding sites). *****