Thymus myosin. Isolation and characterization of myosin from calf thymus and thymic lymphocytes, and studies on the effect of phosphorylation of its Mr = 20,000 light chain.

Regulation of myosin filament assembly by light-chain phosphorylation

“…W hen the light chains are phosphorylated, the M g2+ ATPase activities of both gizzard and thymus myosin are activated approximately 8 to 10-fold by actin (to ca. 160 and 100 nmol Pj mg-1 myosin m in-1 respectively) (Scholey et 1982;Kendrick-Jones et al 1983).…”

“…In the gizzard light chain it has been shown that a single serine residue (19 residues from the N terminus) is phosphorylated (Jakes et al 1976). Structural evidence indicates that the regulatory light chain is located in the neck region of the head, possibly extending across the hinge region between the head and tail (Si-82 junction) portions of the myosin molecule (Flicker et al 1981;V ibert & Craig 1982;Kendrick-Jones et al 1982 a). An intriguing question is how does phosphorylation of the light chain, located in the neck region of the myosin, control not only the interaction of the myosin head with actin but also the interactions in the LM M region of the tail (figure 1), which are believed to be involved in filament formation ?…”

“…When the non-phosphorylated thymus or gizzard myosin filaments are disassembled by stoichiometric levels of Mg-ATP, they disassemble into a single species with a sedimentation coefficient of ca. 1161 (Suzuki et al 1978;Kendrick-Jones et al 1982 Since monomeric myo in high salt concentration sediments with a sedimentation coefficient of 6 it was originally thought that this disassembled species might be a dimer (Suzuki et al 1978;Kendrick-Jones et al 1982 b)and might be the antiparallel dimer that had been suggested as the building bloc for the assembly of smooth muscle and non-muscle myosin filaments (Craig & M egerman 1977;Hinssen et al 1978). It has recently been shown, however, that the disassembled ll-S smooth muscle myosin is monomeric (Trybus et al 1982;Suzuki et al 198 sedim entation coefficient (1LS1 instead of normal monomer 6 appears to be due to a major conformational change in the myosin molecule which reduces its frictional coefficient, i.e.…”

“…An exciting recent finding was the demonstration by Suzuki et al (1978) that phosphorylation of the regulatory light chains of vertebrate smooth-muscle myosin not only initiates myosin interaction with actin but also initiates the assembly of this myosin into filaments. Further studies have shown that light-chain phosphorylation in vitro controls the stability of myosin filaments prepared not only from vertebrate smooth muscle myosins (Suzuki et 1982, Trybus et al 1982Kendrick-Jones et al 1983) but also from vertebrate non-muscle myosins (Scholey et al 1980;M artin et al 1981;Kendrick-Jones et al 1982 In this paper we shall describe our studies aimed at understanding how phosphorylation of the regulatory light chains of vertebrate non-muscle (thymus) and smooth muscle (gizzard) myosins regulates the assembly of these myosins into filaments.…”

Src-dependent NM2A tyrosine-phosphorylation regulates actomyosin dynamics

“…NMHC2A folds into three different domains: the conserved head/motor domain comprising the sites for ATP hydrolysis and actin binding; the neck domain that interacts with the light chains, stabilizing the protein and regulating NM2A activity; and the tail containing a coiled-coil region responsible for heavy chain homodimerization and NMII filament formation [2,3]. Phosphorylation of the RLCs at threonine 18 and serine 19 regulates NM2A enzymatic activity and filament formation [4][5][6][7]. The inactive form of NM2A with unphosphorylated RLCs folds into a compact structure in which motor heads and tails directly interact [2,8,9].…”