2i6u

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{{STRUCTURE_2i6u| PDB=2i6u | SCENE= }}
{{STRUCTURE_2i6u| PDB=2i6u | SCENE= }}
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'''Crystal Structure of Ornithine Carbamoyltransferase complexed with Carbamoyl Phosphate and L-Norvaline from Mycobacterium tuberculosis (Rv1656) at 2.2 A'''
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===Crystal Structure of Ornithine Carbamoyltransferase complexed with Carbamoyl Phosphate and L-Norvaline from Mycobacterium tuberculosis (Rv1656) at 2.2 A===
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==Overview==
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Mycobacterium tuberculosis ornithine carbamoyltransferase (Mtb OTC) catalyzes the sixth step in arginine biosynthesis; it produces citrulline from carbamoyl phosphate (CP) and ornithine (ORN). Here, we report the crystal structures of Mtb OTC in orthorhombic (form I) and hexagonal (form II) space groups. The molecules in form II are complexed with CP and l-norvaline (NVA); the latter is a competitive inhibitor of OTC. The asymmetric unit in form I contains a pseudo hexamer with 32 point group symmetry. The CP and NVA in form II induce a remarkable conformational change in the 80s and the 240s loops with the displacement of these loops towards the active site. The displacement of these loops is strikingly different from that seen in other OTC structures. In addition, the ligands induce a domain closure of 4.4 degrees in form II. Sequence comparison of active-site residues of Mtb OTC with several other OTCs of known structure reveals that they are virtually identical. The interactions involving the active-site residues of Mtb OTC with CP and NVA and a modeling study of ORN in the form II structure strongly rule out an earlier proposed mechanistic role of Cys264 in catalysis and suggest a possible mechanism for OTC. Our results strongly support the view that ORN with an already deprotonated N(epsilon) atom is the species that binds to the enzyme and that one of the phosphate oxygen atoms of CP is likely to be involved in accepting a proton from the doubly protonated N(epsilon) atom of ORN. We have interpreted this deprotonation as part of the collapse of the transition state of the reaction.
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(as it appears on PubMed at http://www.pubmed.gov), where 18062991 is the PubMed ID number.
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{{ABSTRACT_PUBMED_18062991}}
==About this Structure==
==About this Structure==
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[[Category: Tbsgc]]
[[Category: Tbsgc]]
[[Category: X-ray crystallography]]
[[Category: X-ray crystallography]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Wed Apr 30 13:25:44 2008''
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 19:58:21 2008''

Revision as of 16:58, 28 July 2008

Image:2i6u.png

Template:STRUCTURE 2i6u

Crystal Structure of Ornithine Carbamoyltransferase complexed with Carbamoyl Phosphate and L-Norvaline from Mycobacterium tuberculosis (Rv1656) at 2.2 A

Template:ABSTRACT PUBMED 18062991

About this Structure

2I6U is a Single protein structure of sequence from Mycobacterium tuberculosis. Full crystallographic information is available from OCA.

Reference

The crystal structures of ornithine carbamoyltransferase from Mycobacterium tuberculosis and its ternary complex with carbamoyl phosphate and L-norvaline reveal the enzyme's catalytic mechanism., Sankaranarayanan R, Cherney MM, Cherney LT, Garen CR, Moradian F, James MN, J Mol Biol. 2008 Jan 25;375(4):1052-63. Epub 2007 Nov 19. PMID:18062991

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