Distinct Functional Interactions between Actin Isoforms and Nonsarcomeric Myosins

Abstract

Despite their near sequence identity, actin isoforms cannot completely replace each other in vivo and show marked differences in their tissue-specific and subcellular localization. Little is known about isoform-specific differences in their interactions with myosin motors and other actin-binding proteins. Mammalian cytoplasmic β- and γ-actin interact with nonsarcomeric conventional myosins such as the members of the nonmuscle myosin-2 family and myosin-7A. These interactions support a wide range of cellular processes including cytokinesis, maintenance of cell polarity, cell adhesion, migration, and mechano-electrical transduction. To elucidate differences in the ability of isoactins to bind and stimulate the enzymatic activity of individual myosin isoforms, we characterized the interactions of human skeletal muscle α-actin, cytoplasmic β-actin, and cytoplasmic γ-actin with human myosin-7A and nonmuscle myosins-2A, -2B and -2C1. In the case of nonmuscle myosins-2A and -2B, the interaction with either cytoplasmic actin isoform results in 4-fold greater stimulation of myosin ATPase activity than was observed in the presence of α-skeletal muscle actin. Nonmuscle myosin-2C1 is most potently activated by β-actin and myosin-7A by γ-actin. Our results indicate that β- and γ-actin isoforms contribute to the modulation of nonmuscle myosin-2 and myosin-7A activity and thereby to the spatial and temporal regulation of cytoskeletal dynamics. FRET-based analyses show efficient copolymerization abilities for the actin isoforms in vitro. Experiments with hybrid actin filaments show that the extent of actomyosin coupling efficiency can be regulated by the isoform composition of actin filaments.

Various Themes of Myosin Regulation

“…Human nonmuscle myosin-2 isoforms and myosin-7a distinctly interact with isoactins [137]. In vitro , the enzymatic activity of nonmuscle myosin-2a and -2b is 4-fold greater with cytoplasmic β- and γ-actin than with skeletal muscle α-actin, as is the mechanical competence [137].…”

“…In vitro , the enzymatic activity of nonmuscle myosin-2a and -2b is 4-fold greater with cytoplasmic β- and γ-actin than with skeletal muscle α-actin, as is the mechanical competence [137]. The paralog nonmuscle myosin-2c shows the greatest stimulation of its in vitro ATPase activity in the presence of β-actin, as does the myosin-7a:γ-actin pairing [137].…”

“…In vitro , the enzymatic activity of nonmuscle myosin-2a and -2b is 4-fold greater with cytoplasmic β- and γ-actin than with skeletal muscle α-actin, as is the mechanical competence [137]. The paralog nonmuscle myosin-2c shows the greatest stimulation of its in vitro ATPase activity in the presence of β-actin, as does the myosin-7a:γ-actin pairing [137]. In a physiological context, intracellular isoactin:myosin cognate pairs are predicted to locally fine-tune the mechanochemical properties and target the motor to areas with a specialized actin composition such as stress fibers or filopodia.…”

Diatrack particle tracking software: Review of applications and performance evaluation

“…Other in depth investigations of various myosins that exploited Diatrack include those of Weith, Diensthuber, and Chizhov. 34,58,61–65 …”

Actin isoforms and neoplastic transformation

“…Известно о дифференцированном сродстве изоформ актина к ABPs. В экспериментах in vitro показано се-лективное взаимодействие несаркомерных изоформ миозина с изоформами актина [9]. Выявлено пре-имущественное по сравнению с α-скелетным акти-ном взаимодействие цитоплазматических изоформ актина с профилином [10,11], тимозином β4 [12], L-пластином [13], эзрином [14,15], βCAP73 [16], дис трофином и утрофином [17].…”