Substrate-Induced Conformational Change in a Trimeric Ornithine Transcarbamoylase

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 94; no. 18; pp. 9550 - 9555
• Main Authors: Ha, Ya, McCann, Mark T., Tuchman, Mendel, Allewell, Norma M.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 02-09-1997; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences of the USA
• Subjects: Active sites; Amino Acid Sequence; Atomic interactions; Bacteria; Biochemistry; Biological Sciences; Crystal structure; Crystallography, X-Ray; Crystals; Escherichia coli; Escherichia coli - enzymology; Humans; Hydrogen bonds; Molecular Sequence Data; Nitrogen; Ornithine Carbamoyltransferase - chemistry; Oxygen; Protein Conformation; Salts; Solvents; Structure-Activity Relationship; Substrate Specificity; Trimers
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.94.18.9550

The crystal structure of Escherichia coli ornithine transcarbamoylase (OTCase, EC 2.1.3.3) complexed with the bisubstrate analog N-(phosphonacetyl)-L-ornithine (PALO) has been determined at 2.8- angstrom resolution. This research on the structure of a transcarbamoylase catalytic trimer with a substrate analog bound provides new insights into the linkages between substrate binding, protein-protein interactions, and conformational change. The structure was solved by molecular replacement with the Pseudomonas aeruginosa catabolic OTCase catalytic trimer (Villeret, V., Tricot, C., Stalon, V. & Dideberg, O. (1995) Proc. Natl. Acad. Sci. USA 92, 10762-10766; Protein Data Bank reference pdb 1otc) as the model and refined to a crystallographic R value of 21.3%. Each polypeptide chain folds into two domains, a carbamoyl phosphate binding domain and an L-ornithine binding domain. The bound inhibitor interacts with the side chains and/or backbone atoms of Lys-53, Ser-55, Thr-56, Arg-57, Thr-58, Arg-106, His-133, Asn-167, Asp-231, Met-236, Leu-274, Arg-319 as well as Gln-82 and Lys-86 from an adjacent chain. Comparison with the unligated P. aeruginosa catabolic OT-Case structure indicates that binding of the substrate analog results in closure of the two domains of each chain. As in E. coli aspartate transcarbamoylase, the 240s loop undergoes the largest conformational change upon substrate binding. The clinical implications for human OTCase deficiency are discussed.