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Author Notes:
We thank Mr. Mark Frazier and the staff of the Washington University Protein Chemistry Facility for their expert help with peptide synthesis and purification.
The gift of human fibronectin by T. Broeckelmann and J. A. MacDonald is gratefully acknowledged.
We thank Mr. Mitch Vance for assistance in preparation of the polyclonal antibody to peptide II.
Subjects:
Keywords:
- Science & Technology
- Life Sciences & Biomedicine
- Cell Biology
- HUMAN-PLATELET THROMBOSPONDIN
- SMOOTH-MUSCLE CELLS
- AMINO-ACID-SEQUENCE
- MONOCLONAL-ANTIBODIES
- ADHESIVE GLYCOPROTEIN
- ELECTRON-MICROSCOPY
- BINDING SITES
- GROWTH-FACTOR
- MATRIX
- RECEPTOR
The properdin-like type I repeats of human thrombospondin contain a cell attachment site
Abstract:
Thrombospondin (TS) is a modular adhesive glycoprotein that contains three domains previously implicated in the attachment of cells to TS. These include the amino-terminal heparin-binding domain, the carboxy terminal cell or platelet-binding domain, and an RGDA sequence of TS. We have characterized a mAb against human TS, designated A4.1, which inhibits the attachment of human melanoma cells (G361) to TS. The epitope for A4.1 lies within the amino terminal half of the central stalklike region of TS which is distinct from the three known cell attachment sites. This region of TS is recovered in a 50-kD peptide after chymotryptic digestion of TS in EDTA. It contains the procollagen-like domain of TS as well as three type I repeats of a 60-residue segment homologous to two malarial proteins and the complement proteins properdin, and factors C6 through C9. The purified chymotryptic fragment is an effective attachment factor for G361 cells. A4.1 blocks adhesion to the 50-kD domain, as do some sulfated glycoconjugates. RGD (and RGE) peptides and mAbs against other domains of TS are not inhibitory. Peptides (19 mers) based on the core homology sequence of the three type I repeats of TS are potent attachment factors for these cells, and this adhesion is also inhibited by sulfated glycoconjugates. A polyclonal antibody raised against one of these peptides inhibits adhesion of G361 cells to the peptides, to the 50-kD fragment and to intact TS. Thus a new cell-adhesion site has been identified in TS whose sequence is very similar to the site identified in region II of the circumsporozoite protein of malaria parasites (Rich, K.A., F.W. George IV, J.L. Law, and W.J. Martin. 1990. Science (Wash. DC) 249:1574-1577. Thus there may be a common receptor which binds TS, malarial proteins, and properdin.
Copyright information:
The Rockefeller University Press
This is an Open Access work distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License (http://creativecommons.org/licenses/by-nc-sa/4.0/).
