Molecular, genetic and biochemical characterization of lactate dehydrogenase-A enzyme activity mutations in Mus musculus |
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Authors: | Walter Pretsch Bimal Chatterjee Jack Favor Siegbert Merkle Rodica Sandulache |
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Institution: | 1. GSF-National Research Center for Environment and Health, Institute for Mammalian Genetics, Ingolst?dter Landstra?e 1, D-85764, Neuherberg, Germany
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Abstract: | Four independent heterozygous lactate dehydrogenase (LDH) mutations with approximately 60% of wild-type enzyme activity in
whole blood have been recovered. The mutant line Ldh1
a2Neu proved to be homozygous lethal, whereas for the three lines Ldh1
a7Neu, Ldh1
a11Neu, and Ldh1
a12Neu homozygous mutants with about 20% residual activity occurred in the progeny of heterozygous inter se matings. However, the
number of homozygous mutants was less than expected, suggesting an increased lethality of these animals. Various physicochemical
and kinetic properties of LDH are altered. Exons of the Ldh1 gene were PCR amplified and sequenced to determine the molecular lesion in the mutant alleles. Ldh1
a2Neu carried an A/T → G/C transition in codon 112 (in exon 3), resulting in an Asn → Asp substitution; Asn112 is part of the helix
αD, which is involved in the coenzyme-binding domain. Ldh1
a7Neu contained an A/T → C/G transversion within the codon for residue 194 in exon 4, causing an Asp → Ala substitution, which
may affect the arrangement of the substrate-binding site. Three base substituions were discovered for the mutation Ldh1
a11Neu in exon 7: the transition C/G → T/A, a silent mutation, and two transversions C/G → A/T and C/G → G/C, both missense mutations,
which led to the amino acid replacements Ala319 → Glu and Thr321 → Ser, respectively, located in the αH helix structure of
the COOH tail of LDHA. We suggest that the mutation is the result of a gene conversion event between Ldh1
a wild-type gene and the pseudogene Ldh1-ps. The alteration Ile → Thr of codon 241 in exon 6 caused by the base pair change T/A → C/G was identified in the mutation
Ldh1
a12Neu; IIe241 is included in the helix α2G, a structure that is indirectly involved in coenzyme binding. Each of the sequence alterations
has a potential impact on the structure of the LDHA protein, which is consistent with the decreased LDH activity and biochemical
and physiological alterations.
Received: 3 July 1997 / Accepted: 30 September 1997 |
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