Cheng YS, Matusovskiy OS, Rassier DE. Cleavage of loops 1 and 2 in skeletal muscle heavy meromyosin (HMM) leads to a decreased function.
Arch Biochem Biophys 2018;
661:168-177. [PMID:
30465737 DOI:
10.1016/j.abb.2018.11.002]
[Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Revised: 10/31/2018] [Accepted: 11/04/2018] [Indexed: 11/26/2022]
Abstract
BACKGROUND
The mechanical work and the actin-activated ATP kinetics in skeletal muscles are closely associated with two surface loops that are present in the myosin molecule: loop 1 and loop 2. They are located close to the ATP-loop (loop 1), and the actin binding domain (loop 2). In this study we investigated the roles of loops 1 and 2 in the regulation of the load-dependent velocity of actin sliding and ATPase activity.
METHODS
Heavy meromyosin (HMM) from rabbit skeletal muscle was subjected to limited tryptic proteolysis to obtain fragments containing different amounts of loops 1 and 2. The amino-acid sequences of these fragments were confirmed with quantitative mass-spectrometry. The velocity of actin motility propelled by the HMM fragments was measured using in-vitro motility assays, with varying loads induced by the addition of different concentrations of α-actinin.
RESULTS
The load-dependent velocity of the myosin-propelled actin motility, and the fraction of actin filaments motility, were decreased in close association with the depletion of loop 1 in the HMM. The ATPase activity was decreased in close association with depletion of loops 1 and 2.
CONCLUSIONS
Loop 1 is responsible for regulating the load-dependent velocity of actin motility.
GENERAL SIGNIFICANCE
Myosin-actin interaction is closely regulated by two flexible loops in the structure of myosin. The results of this study are important for the understanding of the molecular mechanisms of contraction, and therefore the most basic functions of life, such as locomotion, heart beating, and breathing.
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