Primary structure of murine red blood cell-type pyruvate kinase (PK) and molecular characterization of PK deficiency identified in the CBA strain

Abstract

To clarify the molecular abnormality of pyruvate kinase (PK) deficiency identified in the mutant mice of CBA-Pk-1slc/Pk-1slc, we cloned murine red blood cell-type PK (R-PK) cDNA of those animals. The cDNA sequence spans 1827 bp, including an open reading frame that can encode 574 amino acids. Homology in the coding sequences between murine and human R-PK was 86.1% at nucleotide and 91.5% at amino acid levels. A homozygous missense mutation at nucleotide 1013 GGT-->GAT was identified in the cDNA sequence of the mutant, causing a single amino acid substitution at no. 338Gly-->Asp of the murine R-PK. Six amino acid residues, 335Val-336Ala-337Arg-338Gly-339Asp-340L eu, were encoded in exon 8 of both human and rat L (liver-type)/R-PK genes and were evolutionarily conserved in PK from bacteria through humans. 337Arg was reported to be important for substrate binding, suggesting that the amino acid change would impair substrate affinity of the PK subunit. A homozygous missense mutation at the catalytic domain has been identified in a human PK variant, PK Hong Kong (941ATT-->ACT, 314 Ile-- >Thr). Although both 1013A and 941C gave rise to an amino acid change adjacent to the active site and may interfere with substrate binding to the subunit, the degree of anemia was much more severe in the human case. The erythroid-progenitor cell number increased in the spleen of Pk-1slc/Pk-1slc mice to a level approximately 66 times higher than that in normal CBA mice, suggesting that compensatory extramedullary erythropoiesis in the spleen of the mutant mice, but not in the human variant, might account for the observed difference in the phenotype.