Characterization of human thrombospondin-4.
The thrombospondins are a family of extracellular calcium binding proteins that are involved in cell proliferation, adhesion, and migration. We have sequenced full-length human thrombospondin-4 and characterized the recombinant protein. In contrast to Xenopus laevis thrombospondin-4, the human protein contains an RGD cell binding sequence in the third type 3 repeat. Transfection of mouse NIH3T3 fibroblasts or C2C12 myoblasts with a full-length human thrombospondin-4 cDNA results in the expression of a polypeptide with a reduced molecular weight of 140,000. In the absence of reducing agent, the expressed protein has an apparent molecular weight of 550,000. Recombinant thrombospondin-4 has been purified from the culture supernatant by heparin-Sepharose and anti-thrombospondin-4 antibody-Affi-gel affinity chromatography. Electron microscopy indicates that thrombospondin-4 is composed of five subunits with globular domains at each end. The observation of a calcium-dependent change in the electron microscopic appearance of thrombospondin-4 is consistent with limited tryptic digestion data that indicate that thrombospondin-4 is resistant to digestion in the presence of calcium. These data indicate that thrombospondin-4 is a pentameric protein that binds to heparin and calcium.
Lawler
J
J
Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts 02115.
McHenry
K
K
Duquette
M
M
Derick
L
L
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism* / Q000648:ultrastructure; D003001:Cloning, Molecular; D006801:Humans; D006868:Hydrolysis; D008562:Membrane Glycoproteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism / Q000648:ultrastructure; D019699:Thrombospondins; D014357:Trypsin / Q000378:metabolism; D014982:Xenopus laevis
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D011994:Recombinant Proteins; D019699:Thrombospondins; D014357:Trypsin