Abstract
The three-dimensional structure of actin filaments decorated with the actin-binding domain of chick smooth muscle alpha-actinin (alpha A1-2) has been determined to 21-A resolution. The shape and location of alpha A1-2 was determined by subtracting maps of F-actin from the reconstruction of decorated filaments. alpha A1-2 resembles a bell that measures approximately 38 A at its base and extends 42 A from its base to its tip. In decorated filaments, the base of alpha A1-2 is centered about the outer face of subdomain 2 of actin and contacts subdomain 1 of two neighboring monomers along the long-pitch (two-start) helical strands. Using the atomic model of F-actin (Lorenz, M., D. Popp, and K. C. Holmes. 1993. J. Mol. Biol. 234:826-836.), we have been able to test directly the likelihood that specific actin residues, which have been previously identified by others, interact with alpha A1-2. Our results indicate that residues 86-117 and 350-375 comprise distinct binding sites for alpha-actinin on adjacent actin monomers.
Highlights
The three-dimensional structure of actin filaments decorated with the actin-binding domain of chick smooth muscle c~-actinin(orAl-2) has been determined to 21-/~ resolution
In the presence of the actin-binding domain of c~-actinin, we found that short actin filaments were not uncommon
The actin-binding domain of o~-actinin is an archetype for related domains in a large number of actin crosslinldng proteins, including dystrophin and fimbrin
Summary
The three-dimensional structure of actin filaments decorated with the actin-binding domain of chick smooth muscle c~-actinin(orAl-2) has been determined to 21-/~ resolution. The actin-binding domain is related in sequence to similar-sized domains in dystrophin, spectrin, ABP120, filamin, and fimbrin (de Arruda et al, 1990; Matsudaira, 1991). Together, these proteins form a family of Address all correspondence to Amy McGough, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, 415 South Street, Waltham, MA 02254. The structure of oral-2 is important as an archetype for the interactions of a number of proteins with actin filaments, including severing proteins such as gelsolin. Recent papers on myosin SI interactions with F-actin demonstrate the power of combining the two approaches (Schroder et al, 1993; Raymcnt et al, 1993)
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