Limited digestion of α-actinin in the presence of F-actin.

N-terminal actin-binding domain of α-actinin is connected to central rod domain through flexible neck region that is susceptible to proteolysis. It is suggested that the neck region assumes variable orientations by actin binding. In order to examine the effect of actin binding to α-actinin, we carried out limited digestion of α-actinin by chymotrypsin in the presence and absence of F-actin. Although the cleavage process was retarded when bound to F-actin, digestion to 32 kDa-head and 55 kDa-rod domains occurred through the same intermediate products as the digestion in the absence of F-actin. N-terminal sequencing of 55 kDa-fragment showed the neck region was cleaved at 276-Leu. The cleavage site was not affected by binding to F-actin nor ionic strength of the solvent. It was also indicated that α-actinin was cleaved at 15-Tyr by chymotrypsin. Quantitation of the cleavage products by densitometry of the SDS-gels suggested the conformational change of α-actinin at domain-connecting regions by F-actin binding.