Invertebrate muscles: Thin and thick filament structure; molecular basis of contraction and its regulation, catch and asynchronous muscle

Abstract

This is the second in a series of canonical reviews on invertebrate muscle. We cover here thin and thick filament structure, the molecular basis of force generation and its regulation, and two special properties of some invertebrate muscle, catch and asynchronous muscle. Invertebrate thin filaments resemble vertebrate thin filaments, although helix structure and tropomyosin arrangement show small differences. Invertebrate thick filaments, alternatively, are very different from vertebrate striated thick filaments and show great variation within invertebrates. Part of this diversity stems from variation in paramyosin content, which is greatly increased in very large diameter invertebrate thick filaments. Other of it arises from relatively small changes in filament backbone structure, which results in filaments with grossly similar myosin head placements (rotating crowns of heads every 14.5 nm) but large changes in detail (distances between heads in azimuthal registration varying from three to thousands of crowns). The lever arm basis of force generation is common to both vetebrates and invertebrates, and in some invertebrates this process is understood on the near atomic level. Invertebrate actomyosin is both thin (tropomyosin:troponin) and thick (primarily via direct Ca ++ binding to myosin) filament regulated, and most invertebrate muscles are dually regulated. These mechanisms are well understood on the molecular level, but the behavioral utility of dual regulation is less so. The phosphorylation state of the thick filament associated giant protein, twitchin, has been recently shown to be the molecular basis of catch. The molecular basis of the stretch activation underlying asynchronous muscle activity, however, remains unresolved.

Sea Lily Muscle Lacks a Troponin-Regulatory System, While it Contains Paramyosin

“…Currently, there is no reliable information showing that troponin exists in sea urchin. Ca 2+ sensitive factor(s) for regulation of sea lily muscle probably should be sought in thick filaments or myosin filaments as has been found for many invertebrate animals of protostomes (Lehman and Szent-Gyorgyi, 1975;Hooper et al, 2008).…”

The proteomic response of cheliped myofibril tissue in the eurythermal porcelain crabPetrolisthes cinctipesto heat shock following acclimation to daily temperature fluctuations

“…Whereas the N-terminus of MHCs and MLCs make up the head of the thick filament that forms crossbridges with actin, the C-terminus of MHCs makes up the rod (Clark et al, 2002). Paramyosins are part of the core of the rod in invertebrates (Hooper et al, 2008;Squire, 2009).…”

Lessons from a tarantula: new insights into muscle thick filament and myosin interacting-heads motif structure and function

“…1b) (Huxley and Brown 1967). This model inspired Huxley's seminal ideas on the mechanism of muscular contraction, which he called the swinging, tilting crossbridge-sliding filament mechanism (Huxley 1969(Huxley , 2004b and started the analysis of thick filament structure and function (reviewed by Squire 1975Squire , 1981Squire , 1986Squire , 2009Barral and Epstein 1999;Craig and Padrón 2004;Squire et al 2005;Hooper and Thuma 2005;Craig and Woodhead 2006;Hooper et al 2008;AL-Khayat 2013;Vandenboom 2017).…”