HUMAN ERYTHROCYTE PROTEIN L-ISOASPARTYL METHYLTRANSFERASE - HERITABILITY OF BASAL ACTIVITY AND GENETIC-POLYMORPHISM FOR THERMAL-STABILITY

Protein L-isoaspartyl methyltransferase (PIMT) is believed to play an important role in the disposition of age-damaged proteins by catalyzin g the repair of abnormal isoaspartyl linkages resulting from the spont aneous deamidation of asparaginyl residues or isomerization of asparty l residues, As a step toward testing the hypothesis that human disease -or age-related pathology might be associated with a deficiency in PIM T, we investigated basal activity and thermal stability of PIMT in ery throcyte lysates from 299 U.S. family members, Thermal stability was m easured because it is a sensitive measure of variation in amino acid s equence, Basal activity was normally distributed with a mean +/- SD of 558 +/- 43 units/ml erythrocytes. Statistical analysis of the data re vealed that basal PIMT activity exhibited a high degree of heritabilit y. Enzyme thermal stability showed a skewed bimodall frequency distrib ution, and segregation analysis of family member pedigrees was consist ent with Mendelian inheritance of two major alleles, No DNA was availa ble from the family samples, so we tested two additional population sa mples for a known Ile/Val polymorphism at codon 119 and for PIMT activ ity and thermal stability, using blood donated by 25 Norwegians and by 20 Koreans, Single-stranded conformational polymorphism analysis usin g polymerase chain reaction revealed a 100% correlation between therma l stability grouping and this polymorphism, The high thermal stability samples were all homozygous ne, the low thermal stability samples wer e all homozygous Val, and the intermediate thermal stability samples w ere all heterozygous. Furthermore, this polymorphism was responsible, in part, for the variation observed in basal erythrocyte PIMT activity , These results will help provide a foundation for future studies aime d. It correlating levels of PIMT activity, or other properties of this enzyme, with human disease. (C) 1997 Academic Press.