Characterization of a missense mutation at histidine-44 in a pyruvate dehydrogenase-deficient patient.
Genetic defects in pyruvate dehydrogenase complex (PDC) cause lactic acidosis, neurological deficits, and often early death. Most mutations of PDC are localized in the alpha subunit of the pyruvate dehydrogenase (E1) component. We have kinetically characterized a patient's missense mutation alphaH44R in E1alpha by creating and purifying three recombinant human E1s (alphaH44R, alphaH44Q, and alphaH44A). Substitutions at histidine-15 resulted in decreased V(max) values (6% alphaH44R; 30% alphaH44Q; 90% alphaH44A) while increasing K(m) values for thiamine pyrophosphate (TPP) compared to wild-type (alphaH44R, 3-fold; alphaH44Q, 7-fold; alphaH44A, 10-fold). This suggests that the volume of the residue at site 15 is important for TPP binding and substitution by a residue with a longer side chain disrupts the active site more than the TPP binding site. The rates of phosphorylation and dephosphorylation of alphaH44R E1 by E1-kinase and phospho-E1 phosphatase, respectively, were similar to that of the wild-type E1 protein. These results provide a biochemical basis for altered E1 function in the alphaH44R E1 patient.
Jacobia
Scott J
SJ
Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo 14214, USA.
Korotchkina
Lioubov G
LG
Patel
Mulchand S
MS
D000123:Acetyltransferases / Q000737:chemistry; D001665:Binding Sites; D008058:Dihydrolipoamide Dehydrogenase / Q000737:chemistry; D051047:Dihydrolipoyllysine-Residue Acetyltransferase; D004795:Enzyme Stability; D006801:Humans; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D030481:Pyruvate Dehydrogenase (Lipoamide) / Q000737:chemistry / Q000276:immunology; D011768:Pyruvate Dehydrogenase Complex / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015325:Pyruvate Dehydrogenase Complex Deficiency Disease / Q000201:enzymology / Q000235:genetics*; D013696:Temperature; D013835:Thiamine Pyrophosphate / Q000378:metabolism
D011768:Pyruvate Dehydrogenase Complex; D030481:Pyruvate Dehydrogenase (Lipoamide); D008058:Dihydrolipoamide Dehydrogenase; D000123:Acetyltransferases; D051047:Dihydrolipoyllysine-Residue Acetyltransferase; D013835:Thiamine Pyrophosphate