The covalent maleimidobenzoyl‐actin‐myosin head complex

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Abstract
We have identified the region of actin involved in the covalent coupling of maleimidobenzoyl‐G‐actin to the central 50 kDa segment of the myosin‐S‐1 heavy chain by analyzing the structure of the maleimidobenzoyl‐G‐actin‐S‐1 conjugate using selective proteolytic digestions, amino acid sequence determinations and novel cross‐linking reactions between S‐1 and different maleimidobenzoyl‐G‐actin derivatives. The cross‐linking is shown to occur only on the stretch of residues 48–67 in actin subdomain‐2 with Lys‐50, residing on the outer part of the DNase‐I‐binding loop, as the most likely site of cross‐linking. Because the maleimidobenzoyl‐F‐actin‐S‐1 complex undergoes the same coupling process, the data provide experimental evidence in favor of the recent model of the rigor F‐actin‐S‐1 complex suggesting a close contact between structural elements of the lower domain of the 50 kDa fragment and the top of actin subdomain‐2.