Effect of the N-terminal extension in myosin essential light chain A1 on the mechanism of actomyosin ATP hydrolysis.

Autor: Heeley DH; Department of Biochemistry, Memorial University, St John's, Newfoundland, Canada. Electronic address: dheeley@mun.ca., Belknap B; Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA., Atherton JL; Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA., Hasan SC; Department of Biochemistry, Memorial University, St John's, Newfoundland, Canada., White HD; Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA.
Jazyk: angličtina
Zdroj: The Journal of biological chemistry [J Biol Chem] 2024 Jan; Vol. 300 (1), pp. 105521. Date of Electronic Publication: 2023 Dec 01.
DOI: 10.1016/j.jbc.2023.105521
Abstrakt: Myosin essential light chains A1 and A2 are identical isoforms except for an extension of ∼40 amino acids at the N terminus of A1 that binds F-actin. The extension has no bearing on the burst hydrolysis rate (M-ATP → M-ADP-Pi) as determined by chemical quench flow (100 μM isoenzyme). Whereas actomyosin-S1A2 steady state MgATPase (low ionic strength, 20 °C) is hyperbolically dependent on concentration: V max 7.6 s -1 , K app 6.4 μM (F-actin) and V max 10.1 s -1 , K app 5.5 μM (native thin filaments, pCa 4), the relationship for myosin-S1A1 is bimodal; an initial rise at low concentration followed by a decline to one-third the V max of S1A2, indicative of more than one rate-limiting step and A1-enforced flux through the slower actomyosin-limited hydrolysis pathway. In double-mixing stopped-flow with an indicator, Ca(II)-mediated activation of Pi dissociation (regulatedAM-ADP-Pi → regulatedAM-ADP + Pi) is attenuated by A1 attachment to thin filaments (pCa 4). The maximum accelerated rates of Pi dissociation are: 81 s -1  (S1A1, K app 8.9 μM) versus 129 s -1  (S1A2, K app 58 μM). To investigate apomyosin-S1-mediated activation, thin filaments (EGTA) are premixed with a given isomyosin-S1 and double-mixing is repeated with myosin-S1A1 in the first mix. Similar maximum rates of Pi dissociation are observed, 44.5 s -1  (S1A1) and 47.1 s -1  (S1A2), which are lower than for Ca(II) activation. Overall, these results biochemically demonstrate how the longer light chain A1 can contribute to slower contraction and higher force and the shorter version A2 to faster contraction and lower force, consistent with their distribution in different types of striated muscle.
Competing Interests: Conflict of interest The authors declare that they have no competing interests.
(Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)
Databáze: MEDLINE
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