2HHF

X-ray crystal structure of oxidized human mitochondrial branched chain aminotransferase (hBCATm)

Summary for 2HHF

• Entry DOI: 10.2210/pdb2hhf/pdb
• Related: 1EKF 1EKP 1EKV 1KT8 1KTA 2A1H 2HDK 2HG8 2HGW 2HGX
• Descriptor: Branched-chain-amino-acid aminotransferase, mitochondrial, PYRIDOXAL-5'-PHOSPHATE, 4-(2-HYDROXYETHYL)-1-PIPERAZINE ETHANESULFONIC ACID, ... (5 entities in total)
• Functional Keywords: d-aminoacid aminotransferase-like plp-dependent enzymes, transferase
• Biological source: Homo sapiens (human); More
• Cellular location: Isoform A: Mitochondrion. Isoform B: Cytoplasm: O15382 O15382
• Total number of polymer chains: 2
• Total formula weight: 83598.62

Authors

Yennawar, N.H.,Hutson, S.M. (deposition date: 2006-06-28, release date: 2006-10-24, Last modification date: 2023-11-15)

Primary citation

Yennawar, N.H.,Islam, M.M.,Conway, M.,Wallin, R.,Hutson, S.M.
Human Mitochondrial Branched Chain Aminotransferase Isozyme: STRUCTURAL ROLE OF THE CXXC CENTER IN CATALYSIS.
J.Biol.Chem., 281:39660-39671, 2006

PubMed Abstract: Mammalian branched chain aminotransferases (BCATs) have a unique CXXC center. Kinetic and structural studies of three CXXC center mutants (C315A, C318A, and C315A/C318A) of human mitochondrial (hBCATm) isozyme and the oxidized hBCATm enzyme (hBCATm-Ox) have been used to elucidate the role of this center in hBCATm catalysis. X-ray crystallography revealed that the CXXC motif, through its network of hydrogen bonds, plays a crucial role in orienting the substrate optimally for catalysis. In all structures, there were changes in the structure of the beta-turn preceding the CXXC motif when compared with wild type protein. The N-terminal loop between residues 15 and 32 is flexible in the oxidized and mutant enzymes, the disorder greater in the oxidized protein. Disordering of the N-terminal loop disrupts the integrity of the side chain binding pocket, particularly for the branched chain side chain, less so for the dicarboxylate substrate side chain. The kinetic studies of the mutant and oxidized enzymes support the structural analysis. The kinetic results showed that the predominant effect of oxidation was on the second half-reaction rather than the first half-reaction. The oxidized enzyme was completely inactive, whereas the mutants showed limited activity. Model building of the second half-reaction substrate alpha-ketoisocaproate in the pyridoxamine 5'-phosphate-hBCATm structure suggests that disruption of the CXXC center results in altered substrate orientation and deprotonation of the amino group of pyridoxamine 5'-phosphate, which inhibits catalysis.

PubMed: 17050531
DOI: 10.1074/jbc.M607552200

Experimental method

X-RAY DIFFRACTION (1.8 Å)