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Lauzon, Anne-Marie; Tyska, Matthew J.; Rovner, Arthur S.; Freyzon, Yelena; Warshaw, David M.; Trybus, Kathleen M.

doi:10.1023/a:1005489501357

Cited by 127 publications

(47 citation statements)

References 43 publications

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“…The mechanical properties of these muscles are unknown, but they are used to power crawling at 1 mm⅐s Ϫ1 , 2 with individual contractions visible to the naked eye, and must have much slower contraction velocities than IFMs. The actin velocity on Emb 18 myosin that we have measured more closely resembles those described for phasic smooth muscle isoforms than those of vertebrate slow skeletal muscle isoforms (4,7,8).…”

Section: Discussionsupporting

confidence: 71%

“…The seven-amino acid insert, which determines differences in ATPase rate and in vitro motility velocity between the tonic and phasic smooth muscle isoforms, is not within a homologous region encoded by a Drosophila alternative exon (7,8). Thus, multiple mechanisms appear to have evolved to modify myosin function.…”

Section: Figmentioning

confidence: 99%

“…In phasic smooth muscle myosin, seven additional amino acids near the nucleotide binding site increase actin-activated ATPase rate and in vitro motility velocities compared with the tonic smooth muscle isoform (7,8). Similarly, scallop catch and phasic muscle isoforms have different motility and ATPase rates (9).…”

mentioning

confidence: 99%

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Alternative Exon-encoded Regions of Drosophila Myosin Heavy Chain Modulate ATPase Rates and Actin Sliding Velocity

Swank¹,

Bartoo

Knowles

et al. 2001

Journal of Biological Chemistry

137

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To investigate the molecular functions of the regions encoded by alternative exons from the single Drosophila myosin heavy chain gene, we made the first kinetic measurements of two muscle myosin isoforms that differ in all alternative regions. Myosin was purified from the indirect flight muscles of wild-type and transgenic flies expressing a major embryonic isoform. The in vitro actin sliding velocity on the flight muscle isoform (6.4 m⅐s ؊1 at 22°C) is among the fastest reported for a type II myosin and was 9-fold faster than with the embryonic isoform. With smooth muscle tropomyosin bound to actin, the actin sliding velocity on the embryonic isoform increased 6-fold, whereas that on the flight muscle myosin slightly decreased. No difference in the step sizes of Drosophila and rabbit skeletal myosins were found using optical tweezers, suggesting that the slower in vitro velocity with the embryonic isoform is due to altered kinetics. Basal ATPase rates for flight muscle myosin are higher than those of embryonic and rabbit myosin. These differences explain why the embryonic myosin cannot functionally substitute in vivo for the native flight muscle isoform, and demonstrate that one or more of the five myosin heavy chain alternative exons must influence Drosophila myosin kinetics.

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Section: Discussionsupporting

confidence: 71%

Section: Figmentioning

confidence: 99%

See 1 more Smart Citation

Alternative Exon-encoded Regions of Drosophila Myosin Heavy Chain Modulate ATPase Rates and Actin Sliding Velocity

Swank¹,

Bartoo

Knowles

et al. 2001

Journal of Biological Chemistry

137

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“…The acidic isoform (LC 17a ) is coexpressed with the plus-insert heavy chain whereas the basic isoform (LC 17b ) coexpresses with the minus-insert heavy chain (17)(18)(19). Based on in vitro motility studies, the presence or absence of the sevenamino acid insert in the heavy chain is the sole determinant of the 2-fold faster actin filament velocities for the plus-insert myosin compared with the minus-insert myosin (14,20,21), which in part may contribute to the differences in shortening velocity for phasic and tonic smooth muscles (22,23). The absence of the seven-amino acid insert, in addition to the presence of the LC 17b isoform that is coexpressed with the minusinsert heavy chain (24), may be responsible for the unique ability of the tonic muscle to enter a latch state (25) in which high contractile forces are maintained with minimal expenditure of chemical energy (i.e.…”

mentioning

confidence: 99%

“…The relatively slow actin velocity generated by minus-insert myosin is related in part to the relatively slow ADP release rate of minus-insert myosin (21). Moreover, muscle mechanics and solution biochemical studies suggest that the economic force maintenance of tonic smooth muscle is related to the relatively high ADP affinity of minus-insert myosin, which slows the isometric ATPase rate and prolongs the strongly bound state of myosin at physiological ADP concentrations (8,9,26,27).…”

mentioning

confidence: 99%

The Unique Properties of Tonic Smooth Muscle Emerge from Intrinsic as Well as Intermolecular Behaviors of Myosin Molecules

Baker

Brosseau

Fagnant

et al. 2003

Journal of Biological Chemistry

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To better understand the molecular basis for some of the unique mechanical properties of tonic smooth muscle, we use a laser trap to assay the mechanochemistry of single smooth muscle heavy meromyosin molecules lacking a seven-amino acid insert in the nucleotide binding loop (minus insert). We measured a second-order ATP-induced actin dissociation rate, k T , of 2. , and an ADP affinity, K D , of 3.2 M, which is more than 100-fold greater than that measured for skeletal muscle myosin. By performing in vitro motility studies under nearly identical conditions, we show that the relatively slow actin velocity generated by minus-insert heavy meromyosin is significantly influenced, but not limited, by k ؊D . Our results support a model in which two separate intermediate steps in the actin-myosin catalyzed ATP hydrolysis reaction are energetically coupled through mechanical interactions, and we discuss this model in the context of the ability of tonic muscle to maintain high forces at low energetic cost (latch).Muscle shortening and force generation result from actinmyosin binding events that are coupled to the actin-myosin catalyzed ATP hydrolysis reaction illustrated in Fig. 1. Upon binding to an actin filament (A) and releasing inorganic phosphate (P i ), myosin undergoes a large and discrete rotation of its lever-like light chain domain, which is capable of generating both motion and force (1-5). With the subsequent release of ADP (at the rate k ϪD ) an additional rotation of the light chain domain of myosin has been observed in smooth muscle myosin (6, 7), but unlike the work generating rotation associated with actin binding/P i release, the rotation associated with ADP release is thought to be a strain-sensing biochemical step (8 -10). Following the release of ADP, ATP binding induces the detachment of myosin from the actin filament (at the rate k T ), after which ATP is hydrolyzed.Muscles differ significantly in their shortening speeds and force-generating capacities. For instance, smooth muscle produces a greater average force per myosin and slower speeds of shortening than skeletal muscle (11). To a large extent these mechanical differences are caused by kinetic differences among the different myosin isoforms that exist within different muscle types (12, 13). For example, phasic and tonic smooth muscle (found in the intestine and aorta respectively) express two myosin heavy chain isoforms that differ by a seven-amino acid insert in a surface loop spanning their nucleotide binding pocket (14 -16). Phasic smooth muscle contains primarily the plus-insert myosin, whereas tonic smooth muscle contains primarily the minus-insert myosin. In addition, two essential light chain isoforms are coordinately expressed with the heavy chain isoforms. The acidic isoform (LC 17a ) is coexpressed with the plus-insert heavy chain whereas the basic isoform (LC 17b ) coexpresses with the minus-insert heavy chain (17-19). Based on in vitro motility studies, the presence or absence of the sevenamino acid insert in the heavy chain is t...

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