TY - JOUR
T1 - Human mitochondrial branched chain aminotransferase
T2 - Structural basis for substrate specificity and role of redox active cysteines
AU - Conway, Myra E.
AU - Yennawar, Neela
AU - Wallin, Reidar
AU - Poole, Leslie B.
AU - Hutson, Susan M.
N1 - Funding Information:
This study was supported by a grant from the National Institute of Health to S.M.H. (RO1 DK34738) and an Established Investigatorship from the American Heart Association to L.B.P.
PY - 2003/4/11
Y1 - 2003/4/11
N2 - Crystal structures of the fold type IV pyridoxal phosphate (PLP)-dependent human mitochondrial branched chain aminotransferase (hBCATm) reaction intermediates have provided a structural explanation for the kinetically determined substrate specificity of hBCATm. The isoleucine side chain in the ketimine intermediate occupies a hydrophobic binding pocket that can be defined by three surfaces. Modeling of amino acids on the ketimine structure shows that the side chains of nonsubstrate amino acids such as the aromatic amino acids, alanine, or aspartate either are unable to interact through van der Waals' interactions or have steric clashes. The structural and biochemical basis for the sensitivity of the mammalian BCAT to reducing agents has also been elucidated. Two cysteine residues in hBCATm, Cys315 and Cys318 (CXXC), are part of a redox-controlled mechanism that can regulate hBCATm activity. The residues surrounding Cys315 and Cys318 show considerable sequence conservation in the prokaryotic and eukaryotic BCAT sequences, however, the CXXC motif is found only in the mammalian proteins. The results suggest that the BCAT enzymes may join the list of enzymes that can be regulated by redox status.
AB - Crystal structures of the fold type IV pyridoxal phosphate (PLP)-dependent human mitochondrial branched chain aminotransferase (hBCATm) reaction intermediates have provided a structural explanation for the kinetically determined substrate specificity of hBCATm. The isoleucine side chain in the ketimine intermediate occupies a hydrophobic binding pocket that can be defined by three surfaces. Modeling of amino acids on the ketimine structure shows that the side chains of nonsubstrate amino acids such as the aromatic amino acids, alanine, or aspartate either are unable to interact through van der Waals' interactions or have steric clashes. The structural and biochemical basis for the sensitivity of the mammalian BCAT to reducing agents has also been elucidated. Two cysteine residues in hBCATm, Cys315 and Cys318 (CXXC), are part of a redox-controlled mechanism that can regulate hBCATm activity. The residues surrounding Cys315 and Cys318 show considerable sequence conservation in the prokaryotic and eukaryotic BCAT sequences, however, the CXXC motif is found only in the mammalian proteins. The results suggest that the BCAT enzymes may join the list of enzymes that can be regulated by redox status.
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U2 - 10.1016/S1570-9639(03)00051-7
DO - 10.1016/S1570-9639(03)00051-7
M3 - Article
C2 - 12686109
AN - SCOPUS:1242341233
SN - 1570-9639
VL - 1647
SP - 61
EP - 65
JO - Biochimica et Biophysica Acta - Proteins and Proteomics
JF - Biochimica et Biophysica Acta - Proteins and Proteomics
IS - 1-2
ER -