Conformational changes in subdomain I of actin induced by proteolytic cleavage within the DNase I-binding loop: energy transfer from tryptophan to AEDANS.

Alteration of the actin polypeptide chain within the DNase I-binding loop by cleavage with E. coli A2 protease or subtilisin was shown to increase the efficiency of energy transfer from tryptophan residues to AEDANS attached to Cys-374. Analysis of structural and fluorescence data suggested that only two of four actin tryptophan residues, namely, Trp-340 and/or Trp-356, can be energy transfer donors. It was also found that labelling with AEDANS induces perturbations in the environment of the tryptophan residues, these perturbations being smaller in the cleaved actin. These changes are consistent with a shift of the C-terminal segment of actin monomer upon cleavage and confirm the existence of high conformational coupling between subdomains 1 and 2 of actin monomer. We also suggest that tryptophan residues 340 and/or 356 are located in the focus of this coupling.