Structure of the guanine nucleotide exchange factor Sec7 domain of human Arno and analysis of the interaction with ARF GTPpase

Abstract

Sac7-related guanine nucleotide exchange factors (GEFs) initiate vesicle budding from the Golgi membrane surface by converting the GTPase ARF to a GTPbound, membrane-associated form. Here we report the crystal structure of the catalytic Sac7 homology domain of Arno, a human GEF for ARF1, determined at 2.2 Å resolution. The Sac7 domain is an elongated, all-helical protein with a distinctive hydrophobic groove that is phylogenetically conserved. Structure-based mutagenesis identifies the groove and an adjacent conserved loop as the ARF-interacting surface. The sites of Sec7 domain interaction on ARF1 have subsequently been mapped, by protein footprinting experiments, to the switch 1 and switch..