Crystal structure of SQD1, an enzyme involved in the biosynthesis of the plant sulfolipid headgroup donor UDP-sulfoquinovose

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 96; no. 23; pp. 13097 - 13102
• Main Authors: Mulichak, A.M, Theisen, M.J, Essigmann, B, Benning, C, Garavito, R.M
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 09.11.1999; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Subjects: Arabidopsis Proteins; Arabidopsis thaliana; Atomic interactions; Atoms; Binding Sites; Biochemistry; Biological Sciences; Crystallography, X-Ray; crystals; Enzymes; Enzymes - chemistry; Enzymes - metabolism; Flowers & plants; Glucose; Hydrogen bonds; Hydroxyls; ligands; Models, Molecular; molecular conformation; Molecules; NAD (coenzyme); NAD - metabolism; NADP - metabolism; oxidoreductases; Oxygen; pdb/1qrr; phosphates; phosphates (esters); Plant Proteins - chemistry; Plant Proteins - metabolism; Plants - enzymology; Plants - metabolism; Protein Conformation; Proteins; Sulfur; udp-glucose; Uridine Diphosphate Glucose - analogs & derivatives; Uridine Diphosphate Glucose - biosynthesis; Uridine Diphosphate Glucose - metabolism; X-ray diffraction
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.96.23.13097

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-angstrom 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.