@article{f1ebdc6856514018a33c171ecf99f582,
title = "Interaction Of α-actinin, filamin and tropomyosin with F-actin",
abstract = "The abilities of α-actinin, filamin and tropomyosin to bind F-actin were examined by cosedimentation experiments. Results indicated that smooth muscle α-actinin and filamin can bind to actin filaments simultaneously with little evidence of competition. In contrast, tropomyosin exhibits marked competition with either filamin or α-actinin for sites on actin filaments.",
keywords = "Cell motility, F-Actin, Filamin, Myofibrillar protein, Tropomyosin, α-Actinin",
author = "Zeece, {Michael G.} and Robson, {Richard M.} and Bechtel, {Peter J.}",
note = "Funding Information: incubated with F-actin is shown in Fig. 4. Analysis of the filamin that cosedi-mented with the F-actin pellet in tracks 2, 4 and 6 indicates that ~-actinin had no observable effect on the amount of filamin bound by F-actin, even when the molar ratio of ~-actinin to filamin was 11 : 1. These two experiments (Figs. 3 and 4) taken together indicate that ~-actinin and filamin can simultaneously bind to F-actin and that neither protein could significantly alter binding of the other under these experimental conditions. All the experiments in this study for simultaneous binding of ~-actinin and filamin to F-actin are consistent with reported localization experiments, which have shown that ~-actinin \[17\] and filamin \[14\] are found in both stress fibers and at the cell periphery, and with the possibility that they play a cooperative role in organizing actin filaments \[29\]. In examining the competition between ~-actinin and tropomyosin for binding sites on actin filaments at 23°C, it is interesting that, when ~-actinin is present in great excess, tropomyosin is displaced from the actin pellet. Although it is unlikely that ~-actinin exists in relatively large amounts compared with tropomyosin within the cell as a whole, compartmentalization could create relatively large amounts of one or the other of these proteins in a particular microenvironment. It has been suggested \[1 7\], for instance, that ~-actinin can interact with cellular membranes and presumably form a Z-line analogue through which actin filaments can be attached. Perhaps within the microenvironment of this Z-line analogue, the relative proportion of ~-actinin is large enough to preclude tropomyosin. The results presented here on competition of filamin and tropomyosin for actin binding sites are consistent with the proposal of functionally distinct classes of actin filament \[15\]. For instance, in the highly dynamic class of microfilaments represented by those in the region of membrane ruffles and microspikes of motile cells, filamin is found closely associated with the actin filaments \[14\] whereas tropomyosin is minimally present or absent \[15\]. Consideration of the relative affinities of filamin and tropomyosin for actin filaments and the markedly different results obtained in this study by simply reversing order of addition suggests the possibility that any cytoplasmic event that would permit the presence or availability of only one protein or the other during a crucial period of assembly of actin filaments could result in distinct functional classes of actin filaments. During the latter stages of this study, results concerning competition of filamin and tropomyosin for F-actin were published \[30\].A lthough the investigators used a quite different technique, flow birefringence, their results also demonstrated competition between tropomyosin and filamin for binding to F-actin, in general agreement with the related portion of our co-sedimentation studies. We are grateful to Dr. Marvin H. Stromer and Randy DenAdel for help in preparation of the figures, to Mary Bremner and Jo Sprague for help in preparation of the proteins, and to Joan Andersen for help with this manuscript. This work was supported in part by a grant from the National Institutes of Health (HL15679) and by grants from the Muscular Dystrophy Association Of America and the American and Iowa Heart Associations.",
year = "1979",
month = dec,
day = "14",
doi = "10.1016/0005-2795(79)90258-7",
language = "English (US)",
volume = "581",
pages = "365--370",
journal = "BBA - Protein Structure",
issn = "1570-9639",
publisher = "Elsevier",
number = "2",
}