| Abstract |
Prolidase deficiency (MIM 26413), an autosomal recessive phenotype, is
caused by rare alleles at a locus on chromosome 19cent-q13.2. The clinical
phenotype is pleiotropic (affecting skin, brain, etc.) and of variable
expressivity (benign to early death). I established skin fibroblast
cultures from 6 homozygous probands and 6 obligate heterozygotes, purified
prolidase (E.C. 3.4.13.9, a homodimer) from normal human fibroblasts,
raised a monospecific rabbit antiserum to the subunit, and studied its
biosynthesis. Pulse-chase immunoprecipitation experiments showed that the
subunit is synthesized in the cytosol as a 58 KDa. polypeptide and not
processed further. Homozygous prolidase-deficient cell strains expressed 3
classes of mutant alleles which by complementation analysis mapped to one
locus. The alleles were designated CRM-(nul), CRM+ activity/size variant,
and CRM+ activity variant. Heterozygotes carrying CRM- alleles have heat
stable prolidase (50 Celsius, 1hr); heterozygotes carrying CRM+ variant
alleles have heat labile enzyme. The finding implies that variant CRM+
allele(s) can confer negative allelic complementation on the dimeric
enzyme (dominant relative phenotype). CRM- homozygous cells contain varying
amounts of an alternative imidodipeptidase-like activity. The variant
prolidase allele (major gene) and amount of alternative "prolidase"
activity (modifier gene) are apparently both determinants of the
associated clinical phenotype in prolidase deficiency. I obtained and
sequenced a tryptic peptide from human kidney prolidase for synthesis of
oligonucleotide probes in the future.
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