STRUCTURE OF THROMBOSPONDIN

  • 1 January 1984
    • journal article
    • research article
    • Vol. 259  (6) , 3944-3948
Abstract
The NH2-terminal amino acid sequences of [human] thrombospondin and of a 30,000-Da [dalton] heparin-binding peptide derived from thrombospondin by treatment with plasmin are identical. The heparin-binding peptide is homogeneous in size but slightly heterogeneous in charge with the predominant isoelectric points being 6.1 and 5.7. EM of tungsten replicas of thrombospondin reveals a tripartite structure resembling a bola which is about 60 nm across when fully extended. Each part of the molecule terminates in a globular node or head which disappears upon limited plasmin digestion, suggesting that the heparin-binding peptide is located in the head region. In addition to the heparin-binding peptide, a 20,000-Da peptide also apparently associated with the head region is liberated during proteolysis. The EM indicate that the legs of the bola-like structure must be folded into an extended, flexible tertiary structure. These legs, each of about 65,000 Da, appear to be attached near the ends opposite the heads, probably by disulfide bonds. Each leg possesses a tab of protein (.apprx. 20,000 Da) which juts out from this attachment point.