Molecular characterization of genetic mutations in human lactate dehydrogenase (LDH) B (H) variant.
We have previously detected a single base substitution of G by A at the Arg codon CGC in exon 4 of the mutant lactate dehydrogenase (LDH) gene, an unstable LDH-B variant (case 1). Here, we use the polymerase chain reaction (PCR) to amplify genomic DNA of two cases (the original case 1 and a new patient, case 2). We were able to confirm that case 1 is homozygous for the mutation, causing a replacement of the conserved Arg by His at residue 173. The resulting LDH-B variant subunit is unstable in vivo. Whereas the mutation in exon 4 was not observed in case 2, a different single base substitution of A by C was detected at the Ser codon AGT in exon 3. This mutation causes a replacement of the conserved Ser by Arg at residue 131. Genomic analysis of the family of case 2 by mismatched PCR showed that the missense mutation was consistent with their biochemical phenotypes. The replacement results in a conformational change of the residues near the Ser, probably because the side chain of Arg is much more bulky than that of Ser. The change may affect the arrangement of the cofactor binding site and result in the loss of enzyme activity. The experimental observations are consistent with computer graphics analyses.
Sudo
K
K
Department of Laboratory Medicine, Jikei University School of Medicine, Daisan Hospital, Komae, Japan.
Maekawa
M
M
Tomonaga
A
A
Tsukada
T
T
Nakayama
T
T
Kitamura
M
M
Li
S S
SS
Kanno
T
T
Toriumi
J
J
D000595:Amino Acid Sequence; D001483:Base Sequence; D014644:Genetic Variation / Q000235:genetics; D006801:Humans; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase / Q000737:chemistry / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009838:Oligodeoxyribonucleotides / Q000235:genetics; D010375:Pedigree; D016133:Polymerase Chain Reaction; D011487:Protein Conformation
D007527:Isoenzymes; D009838:Oligodeoxyribonucleotides; D007770:L-Lactate Dehydrogenase