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Structure of a thrombospondin C-terminal fragment reveals a novel calcium core in the type 3 repeats

Marc Kvansakul1, Josephine C Adams, Erhard Hohenester

  • 1Department of Biological Sciences, Imperial College London, South Kensington Campus, London, UK.

The EMBO Journal
|March 12, 2004
PubMed

Insights

Thrombospondins (TSPs) are extracellular proteins regulated by calcium. Their structure, particularly calcium-binding sites in T3 repeats and CTD, is crucial for cell interactions and stability.

Area of Science:

  • Biochemistry
  • Structural Biology
  • Cell Biology

Background:

  • Thrombospondins (TSPs) are extracellular matrix proteins regulating cell behavior.
  • The Type 3 (T3) repeats and C-terminal globular domain (CTD) are highly conserved regions in TSPs.
  • Calcium ions play a critical role in TSP structure and function.

Purpose of the Study:

  • To determine the crystal structure of a cell-binding TSP-1 fragment containing T3 repeats and CTD.
  • To elucidate the role of calcium ions in the structural organization and function of the TSP C-terminal region.
  • To understand how mutations in T3 repeats affect TSP structure and are linked to skeletal disorders.

Main Methods:

  • X-ray crystallography to determine the structure of a TSP-1 fragment.
  • Analysis of calcium-binding motifs (DxDxDGxxDxxD) within T3 repeats.
  • Investigating the impact of structural disruptions on protein secretion and stability.
  • Assessing calcium modulation of cell-binding RGD motifs.

Main Results:

  • The crystal structure revealed a compact assembly of three T3 repeats and the CTD.
  • T3 repeats lack secondary structure and organize around calcium ions via novel binding motifs.
  • The CTD forms a lectin-like beta-sandwich with four conserved calcium-binding sites.
  • Disrupting T3 repeat structure reduced protein secretion and stability.
  • Calcium loading modulates the availability of an RGD cell-attachment site.

Conclusions:

  • Calcium ions are central to the architecture and function of the TSP C-terminal region.
  • The structural integrity of T3 repeats and CTD, stabilized by calcium, is essential for TSP stability and function.
  • Mutations affecting T3 repeats in TSP-5/COMP likely disrupt the T3-CTD assembly, explaining associated skeletal disorders.

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