title: Structure of a loose dimer: an intermediate in nitric oxide synthase assembly.
abstract: Cooperativity among ligand binding, subunit association, and protein folding has implications for enzyme regulation as well as protein aggregation events associated with disease. The binding of substrate l-arginine or cofactor tetrahydrobiopterin converts nitric oxide synthases (NOSs) from a "loose dimer", with an exposed active center and higher sensitivity to proteolysis, to a "tight dimer" competent for catalysis. The crystallographic structure of the Bacillus subtilis NOS loose dimer shows an altered association state with severely destabilized subdomains. Ligand binding or heme reduction converts loose dimers to tight dimers in solution and crystals. Mutations at key positions in the dimer interface that distinguish prokaryotic from eukaryotic NOSs affect the propensity to form loose dimers. The loose dimer structure indicates that non-native interactions can mediate subunit association in NOS.
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University Ithaca, NY 14853, USA.
authors.forename: Kartikeya
authors.initials: K
authors.lastname: Pant
authors.forename: Brian R
authors.initials: BR
authors.lastname: Crane
mesh_terms: D000818:Animals; D001412:Bacillus subtilis / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019001:Nitric Oxide Synthase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D021122:Protein Subunits; D019001:Nitric Oxide Synthase