cDNA cloning, genomic organization and expression of the novel human metallophosphoesterase gene MPPE1 on chromosome 18p11.2.

We have isolated a 1,926-bp cDNA that encodes a novel polypeptide of 396 amino acid residues with a calculated molecular mass of 45.2 kDa. This MPPE1 polypeptide consists of a predicted signal sequence of 45 residues at the N-terminus, a 240-amino acid metallo-phosphoesterase domain, and a 24-amino acid transmembrane domain at the C-terminus. The genomic organization of the human MPPE1 gene proved to consist of 14 exons and to span about 27 kb. The gene was located on chromosome 18p11.2, adjacent to the G protein Golf alpha gene (GNAL), in tail-to-tail orientation, partially overlapping with the 3' UTR of the latter gene. MPPE1 is expressed as an mRNA of 2.2 kb in the brain, but not in any other tissues studied here. 3' RACE analysis defined a single functional polyadenylation site within the 3' UTR of the GNAL gene, while RT-PCR analysis revealed an alternatively spliced form of MPPE1, which included an additional exon located within the last intron. The alternatively spliced form encoded a truncated variant of MPPE1 with a calculated molecular mass of 38.8 kDa that lacks the C-terminal transmembrane domain.