TY - JOUR
T1 - Structural and biochemical basis for novel mutations in homozygous Israeli maple syrup urine disease patients
T2 - A proposed mechanism for the thiamin-responsive phenotype
AU - Chuang, Jacinta L.
AU - Wynn, R. Max
AU - Moss, Clint C.
AU - Song, Jiu Li
AU - Li, Jun
AU - Awad, Nibal
AU - Mandel, Hanna
AU - Chuang, David T.
PY - 2004/4/23
Y1 - 2004/4/23
N2 - Maple syrup urine disease (MSUD) results from mutations affecting different subunits of the mitochondrial branched-chain α-ketoacid dehydrogenase complex. In this study, we identified seven novel mutations in MSUD patients from Israel. These include C219W-α (TGC to TGG) in the E1α subunit; H156Y-β (CAT to TAT), V69G-β (GTT to GGT), IVS 9 del[-7:-4], and 1109 ins 8bp (exon 10) in the E1β subunit; and H391R (CAC to CGC) and S133stop (TCA to TGA) affecting the E2 subunit of the branched-chain α-ketoacid dehydrogenase complex. Recombinant E1 proteins carrying the C219W-α or H156Y-β mutation show no catalytic activity with defective subunit assembly and reduced binding affinity for cofactor thiamin diphosphate. The mutant E1 harboring the V69G-β substitution cannot be expressed, suggesting aberrant folding caused by this mutation. These E1 mutations are ubiquitously associated with the classic phenotype in homozygous-affected patients. The H391R substitution in the E2 subunit abolishes the key catalytic residue that functions as a general base in the acyltransfer reaction, resulting in a completely inactive E2 component. However, wild-type E1 activity is enhanced by E1 binding to this full-length mutant E2 in vitro. We propose that the augmented E1 activity is responsible for robust thiamin responsiveness in homozygous patients carrying the H391R E2 mutation and that the presence of a full-length mutant E2 is diagnostic of this MSUD phenotype. The present results offer a structural and biochemical basis for these novel mutations and will facilitate DNA-based diagnosis for MSUD in the Israeli population.
AB - Maple syrup urine disease (MSUD) results from mutations affecting different subunits of the mitochondrial branched-chain α-ketoacid dehydrogenase complex. In this study, we identified seven novel mutations in MSUD patients from Israel. These include C219W-α (TGC to TGG) in the E1α subunit; H156Y-β (CAT to TAT), V69G-β (GTT to GGT), IVS 9 del[-7:-4], and 1109 ins 8bp (exon 10) in the E1β subunit; and H391R (CAC to CGC) and S133stop (TCA to TGA) affecting the E2 subunit of the branched-chain α-ketoacid dehydrogenase complex. Recombinant E1 proteins carrying the C219W-α or H156Y-β mutation show no catalytic activity with defective subunit assembly and reduced binding affinity for cofactor thiamin diphosphate. The mutant E1 harboring the V69G-β substitution cannot be expressed, suggesting aberrant folding caused by this mutation. These E1 mutations are ubiquitously associated with the classic phenotype in homozygous-affected patients. The H391R substitution in the E2 subunit abolishes the key catalytic residue that functions as a general base in the acyltransfer reaction, resulting in a completely inactive E2 component. However, wild-type E1 activity is enhanced by E1 binding to this full-length mutant E2 in vitro. We propose that the augmented E1 activity is responsible for robust thiamin responsiveness in homozygous patients carrying the H391R E2 mutation and that the presence of a full-length mutant E2 is diagnostic of this MSUD phenotype. The present results offer a structural and biochemical basis for these novel mutations and will facilitate DNA-based diagnosis for MSUD in the Israeli population.
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U2 - 10.1074/jbc.M313879200
DO - 10.1074/jbc.M313879200
M3 - Article
C2 - 14742428
AN - SCOPUS:2342434850
SN - 0021-9258
VL - 279
SP - 17792
EP - 17800
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 17
ER -