Scheme of rat PC cDNA and predicted protein
structure. (A) Restriction enzyme map of rat PC cDNA showing the 5′ and
3′ untranslated regions and coding region (box). (B) Scheme of the
comparative protein structure of rat, rabbit, human, and chicken PC.
The rat PC cDNA is ∼5.5 kb with an ORF encoding 485 aa. The primary
structure of rat PC predicts a type 1 transmembrane protein consisting
of a putative 24-aa N-terminal signal peptide sequence (striped box), a
360-aa ectodomain, a 26-aa single transmembrane-spanning domain
(hatched box), and a 75-aa C-terminal cytoplasmic tail. The ectodomain
of rat PC is shorter than that of PC from other species. It has seven
potential sites for N-linked glycosylation (arrowheads)
and numerous potential sites for O-linked glycosylation
(○). Four cysteines (★) for potential disulfide linkage believed
to form two loop structures are conserved in all species. The
percentages of amino acid identity between the ectodomains or
transmembrane and cytoplasmic domains of rat PC and those of PC from
other species are shown.