TY - JOUR
T1 - Structural Analyses of a Malate Dehydrogenase with a Variable Active Site
AU - Bell, Jessica K.
AU - Yennawar, Hemant P.
AU - Wright, S. Kirk
AU - Thompson, James R.
AU - Viola, Ronald E.
AU - Banaszak, Leonard J.
PY - 2001/8/17
Y1 - 2001/8/17
N2 - Malate dehydrogenase specifically oxidizes malate to oxaloacetate. The specificity arises from three arginines in the active site pocket that coordinate the carboxyl groups of the substrate and stabilize the newly forming hydroxyl/keto group during catalysis. Here, the role of Arg-153 in distinguishing substrate specificity is examined by the mutant R153C. The x-ray structure of the NAD binary complex at 2.1 Å reveals two sulfate ions bound in the closed form of the active site. The sulfate that occupies the substrate binding site has been translated ∼2 Å toward the opening of the active site cavity. Its new location suggests that the low catalytic turnover observed in the R153C mutant may be due to misalignment of the hydroxyl or ketone group of the substrate with the appropriate catalytic residues. In the NAD-pyruvate ternary complex, the monocarboxylic inhibitor is bound in the open conformation of the active site. The pyruvate is coordinated not by the active site arginines, but through weak hydrogen bonds to the amide backbone. Energy minimized molecular models of unnatural analogues of R153C (Wright, S. K., and Viola, R. E. (2001) J. Biol. Chem. 276, 31151-31155) reveal that the regenerated amino and amido side chains can form favorable hydrogen-bonding interactions with the substrate, although a return to native enzymatic activity is not observed. The low activity of the modified R153C enzymes suggests that precise positioning of the guanidino side chain is essential for optimal orientation of the substrate.
AB - Malate dehydrogenase specifically oxidizes malate to oxaloacetate. The specificity arises from three arginines in the active site pocket that coordinate the carboxyl groups of the substrate and stabilize the newly forming hydroxyl/keto group during catalysis. Here, the role of Arg-153 in distinguishing substrate specificity is examined by the mutant R153C. The x-ray structure of the NAD binary complex at 2.1 Å reveals two sulfate ions bound in the closed form of the active site. The sulfate that occupies the substrate binding site has been translated ∼2 Å toward the opening of the active site cavity. Its new location suggests that the low catalytic turnover observed in the R153C mutant may be due to misalignment of the hydroxyl or ketone group of the substrate with the appropriate catalytic residues. In the NAD-pyruvate ternary complex, the monocarboxylic inhibitor is bound in the open conformation of the active site. The pyruvate is coordinated not by the active site arginines, but through weak hydrogen bonds to the amide backbone. Energy minimized molecular models of unnatural analogues of R153C (Wright, S. K., and Viola, R. E. (2001) J. Biol. Chem. 276, 31151-31155) reveal that the regenerated amino and amido side chains can form favorable hydrogen-bonding interactions with the substrate, although a return to native enzymatic activity is not observed. The low activity of the modified R153C enzymes suggests that precise positioning of the guanidino side chain is essential for optimal orientation of the substrate.
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U2 - 10.1074/jbc.M100902200
DO - 10.1074/jbc.M100902200
M3 - Article
C2 - 11389141
AN - SCOPUS:0035903166
SN - 0021-9258
VL - 276
SP - 31156
EP - 31162
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 33
ER -