title: Purification and characterization of the catalytic domains of the human receptor-linked protein tyrosine phosphatases HPTP beta, leukocyte common antigen (LCA), and leukocyte common antigen-related molecule (LAR).
abstract: Human HPTP beta, leukocyte common antigen (LCA), and leukocyte common antigen-related molecule (LAR) are transmembrane receptor-like proteins whose cytoplasmic regions contain either one (HPTP beta) or two (LCA and LAR) domains that are homologous to protein tyrosine phosphatases (PTPases). Whereas the membrane-proximal domain 1 has enzymatic activity, the membrane-distal domain 2 of both LCA and LAR has no detectable catalytic activity. The cytoplasmic regions of HPTP beta, LCA, and LAR were expressed in Escherichia coli and purified to greater than 90% purity. Modulatory effects of various low molecular weight compounds and homo- and copolymers of amino acids were examined. Several polypeptides that contain a high proportion of tyrosine were strongly inhibitory to these PTPases. To determine a possible role for the LAR domain 2, the properties of recombinant LAR PTPases containing both domains 1 and 2 (LAR-D1D2) or only domain 1 (LAR-D1) were compared. In nearly all aspects examined, LAR-D1 and LAR-D1D2 were indistinguishable. However, polycationic polypeptides strongly stimulated the PTPase activity of LAR-D1D2, but not LAR-D1, using the peptide substrate Raytide. Thus, basic polypeptides seem to indirectly alter the catalytic activity of domain 1 by interacting with domain 2. This result suggests that domain 2 has a regulatory function.
authors.affiliation: Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115.
authors.forename: M
authors.initials: M
authors.lastname: Itoh
authors.forename: M
authors.initials: M
authors.lastname: Streuli
authors.forename: N X
authors.initials: NX
authors.lastname: Krueger
authors.forename: H
authors.initials: H
authors.lastname: Saito
mesh_terms: D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000302:isolation & purification / Q000378:metabolism*; D002384:Catalysis; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics; D006023:Glycoproteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006649:Histocompatibility Antigens / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017493:Leukocyte Common Antigens; D008969:Molecular Sequence Data; D010957:Plasmids; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4; D011956:Receptors, Cell Surface / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D006023:Glycoproteins; D006649:Histocompatibility Antigens; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D017493:Leukocyte Common Antigens; C516841:PTPRA protein, human; D017027:Protein Tyrosine Phosphatases; D054630:Receptor-Like Protein Tyrosine Phosphatases, Class 4