title: Prokaryotic expression of the heme- and flavin-binding domains of rat neuronal nitric oxide synthase as distinct polypeptides: identification of the heme-binding proximal thiolate ligand as cysteine-415.
abstract: The heme- and flavin-binding domains of constitutive rat neuronal nitric oxide synthase (NOS) were expressed in Escherichia coli as distinct polypeptides with properties characteristic of the intact enzyme. The amino-terminal heme-binding domain (residues 1-714) was expressed using the expression vector pCW. The denatured molecular mass of the expressed protein was 80 kDa, and the protein was shown to be immunoreactive to rabbit anti-NOS IgG. The NOS hemoprotein exhibited a ferrous-carbon monoxide difference spectrum with a wavelength maximum at 445 nm. Spectral perturbation with L-arginine and BH4 elicited a type I difference spectrum, confirming the presence of binding sites for these molecules within the N-terminal NOS polypeptide. Site-directed mutagenesis was applied to the putative axial heme ligand, cysteine-415, generating the histidine mutant, which confirmed the identity of the proximal ligand. NOS flavoproteins, with (C1, residues 715-1429) and without (C2, residues 749-1429) an amino-terminal calmodulin-binding motif, were expressed using the vector pPROK-1. The C1 and C2 flavoproteins were immunoreactive to anti-NOS IgG and were sized at approximately 80 kDa. Both of the purified flavoproteins exhibited optical absorbance properties typical of a flavin prosthetic group, with wavelength maxima at 380 and 450 nm, and were competent in NADPH-dependent electron transfer to cytochrome c, with observed rates of approximately 2-4 mumol/min/mg. The bacterial expression of the NO synthase heme-binding oxygenase and flavoprotein oxidoreductase domains as isolated proteins with specific properties of the intact enzyme represents an important development in structure-function studies of this complex enzyme.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center at San Antonio 78284-7760.
authors.forename: K
authors.initials: K
authors.lastname: McMillan
authors.forename: B S
authors.initials: BS
authors.lastname: Masters
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D003545:Cysteine / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D004926:Escherichia coli / Q000235:genetics; D005415:Flavins / Q000378:metabolism*; D006418:Heme / Q000378:metabolism*; D006420:Hemeproteins / Q000235:genetics / Q000378:metabolism; D006639:Histidine / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009474:Neurons / Q000201:enzymology*; D019001:Nitric Oxide Synthase; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D051381:Rats
chemical_list: D017931:DNA Primers; D005415:Flavins; D006420:Hemeproteins; D010455:Peptides; D006418:Heme; D006639:Histidine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; D003545:Cysteine