title: Crystal structure of SQD1, an enzyme involved in the biosynthesis of the plant sulfolipid headgroup donor UDP-sulfoquinovose.
abstract: The SQD1 enzyme is believed to be involved in the biosynthesis of the sulfoquinovosyl headgroup of plant sulfolipids, catalyzing the transfer of SO(3)(-) to UDP-glucose. We have determined the structure of the complex of SQD1 from Arabidopsis thaliana with NAD(+) and the putative substrate UDP-glucose at 1.6-A resolution. Both bound ligands are completely buried within the binding cleft, along with an internal solvent cavity which is the likely binding site for the, as yet, unidentified sulfur-donor substrate. SQD1 is a member of the short-chain dehydrogenase/reductase (SDR) family of enzymes, and its structure shows a conservation of the SDR catalytic residues. Among several highly conserved catalytic residues, Thr-145 forms unusually short hydrogen bonds with both susceptible hydroxyls of UDP-glucose. A His side chain may also be catalytically important in the sulfonation.
authors.affiliation: Department of Biochemistry, Michigan State University, East Lansing, MI 48824-1319, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Mulichak
authors.forename: M J
authors.initials: MJ
authors.lastname: Theisen
authors.forename: B
authors.initials: B
authors.lastname: Essigmann
authors.forename: C
authors.initials: C
authors.lastname: Benning
authors.forename: R M
authors.initials: RM
authors.lastname: Garavito
mesh_terms: D029681:Arabidopsis Proteins; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004798:Enzymes / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D010944:Plants / Q000201:enzymology / Q000378:metabolism*; D011487:Protein Conformation; D014532:Uridine Diphosphate Glucose / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D004798:Enzymes; D010940:Plant Proteins; C110849:SQD1 protein, Arabidopsis; C096386:uridine diphosphate sulfoquinovose; D009243:NAD; D009249:NADP; D014532:Uridine Diphosphate Glucose