The conformation of the C-terminal region of actin: A site-specific photocrosslinking study using benzophenone-4-maleimide

Abstract

The site-specific photocrosslinker, benzophenone-4-maleimide, was used to label G-actin specifically at Cys-374, the penultimate residue from the C terminus. The resultant BP-G-actin was polymerized to form BP-F-actin, and both forms of actin were irradiated to activate the benzophenone moiety. We found that for BP-F-actin both intersubunit and intrasubunit photocrosslinks were formed. For BP-G-actin only a small amount of an internally photocrosslinked species was formed. These findings suggest that in the F-actin polymer, the C-terminal peptide is localized in a region between neighboring subunits. In contrast, in the G-actin monomer, the C-terminal peptide is relatively distant from the surface of the molecule.