Isolation of cDNAs Encoding Gibbon and Monkey Platelet and T Cell Activation Antigen 1 (PTA1)

Abstract

Human platelet and T cell activation antigen 1 (PTA1) is a 67kDa type I transmembrane glycoprotein mainly expressed on the surface of activated T cells and platelets, and is involved in the development of human cytotoxic T cell (CTL) as well as platelet activation and aggregation. We have cloned and sequenced gibbon PTA1 (gPTAl) and monkey PTA1 (mPTA1) cDNAs by RT-PCR from gibbon leukemic cell line MLA 144 and PHA-induced Rhesus monkey PBMC respectively. The mature proteins of gPTA1, mPTA1 and human PTA1 (hPTA1) share 93–95% amino acid similarity with the highest similarity in domain 1 of extracellular region. All the important features of PTA1 molecule are conserved among these Primates: (1) the ORF encoding 336 amino acid residues including signal sequence (18aa). extracellular region (232aa), transmembrane sequence (25aa) and cytoplasmic region (61aa); (2) two conserved pairs of Cys (Cys¹⁹ to Cys⁹⁰and Cys¹³⁴ to Cys²⁰⁴) forming disulfide bonds stabilizing the two immunoglobulin superfamily V-like domains; (3) eight putative N-linked glycosylation sites (except gPTA1 with nine sites) and three O-linked glycosylation sites in extracellular region; and (4) predicated protein kinase C phosphorylation sites (Thr²⁷⁵ and Ser³¹¹), casein kinase II sites (Ser²⁹⁵ and The²⁹⁹) and the potential tyrosine phosphorylation site (Tyr³⁰⁴). These data indicate that PTA1 molecule is highly conserved among the Primates and may play important roles in immune response.

Key Words:

• Leukocyte differentiation antigen
• Immunoglobulin superfamily
• Adhesion molecule
• Primates
• PBMC
• Monoclonal antibody
• RT-PCR
• Homology