Structural characterization of cyclase-associated protein (CAP) domains

Abstract

Cyclase-associated protein (CAP) is a highly conserved and widely distributed protein required for normal cell growth and development. In yeast, CAP is a component of the adenylyl cyclase complex and helps to activate the Ras-mediated catalytic cycle of the cyclase. Full-length CAP constitutes an N-terminal domain (N-CAP), required for Ras response, a C-terminal domain (C-CAP), that interacts with the cytoskeleton, and a proline-rich middle domain, which can bind to SH3 domains. N-CAP and C-CAP have been shown to be dimeric in their crystal structures [1, 2]. Our own crystallographic studies on N-CAP from Dictyostelium discoideum [3, 4] have revealed the presence of both a head-to-tail dimer conformation, along with the previously reported side-to-side dimer [1]. These interactions are indicative of the variable modes of oligomerization, which makes studies on full-length CAP difficult to perform. We present the results of experiments to elucidate the oligomerization behaviour of CAP in solution and their comparison to findings from the crystal structures.