Identification of Base Substitutions in Ten Types of Rare Variants of Phosphoglucomutase-1 (PGM1) Encountered in Japanese

In a previous starch-gel electrophoresis study of erythrocyte phosphoglucomutase-1 (PGM1) in 23,095 Japanese from Hiroshima and Nagasaki, we detected 14 types of rare variant alleles. To determine sequence differences in these rare alleles, cell lines were established from peripheral Blymphocytes from 24 unrelated individuals in whom nine types of rare variants are presumed to exist on the basis of earlier electrophoresis studies. cDNAs reverse transcribed from mRNAs extracted from these cell lines were amplified by polymerase chain reaction and sequences determined. Amino acid substitution types were deduced from each cDNA sequence. Although two individuals were reported to have an identical electromorph (PGM1 4HR3), sequence analysis revealed that alleles encoding these electromorphs possessed different base substitutions, and one was renamed PGM1 4HR4. As the amino acid substitution of ten different variants could be deduced by cDNA sequence in this study, the effect of each amino acid substitution on enzyme activity could be precisely simulated. The secondary structure of each variant predicted by computer simulations revealed that very decreased activity observed on PGM1 4HR2 protein was caused by significant secondary structure change introduced by the amino acid substitution. On the basis of the crystal structure, the amino acid substitutions of the ten types of rare variants seem to be outside the active center of this enzyme