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Crystal structure of the angiogenesis inhibitor endostatin at 1.5 A resolution
E Hohenester1, T Sasaki, B R Olsen
1Department of Crystallography, Birkbeck College, London WC1E 7HX, UK. e.hohenester.cryst.bbk.ac.uk
Abstract:
A number of extracellular proteins contain cryptic inhibitors of angiogenesis. Endostatin is a 20 kDa C-terminal proteolytic fragment of collagen XVIII that potently inhibits endothelial cell proliferation and angiogenesis. Therapy of experimental cancer with endostatin leads to tumour dormancy and does not induce resistance. We have expressed recombinant mouse endostatin and determined its crystal structure at 1.5 A resolution. The structure reveals a compact fold distantly related to the C-type lectin carbohydrate recognition domain and the hyaluronan-binding Link module. The high affinity of endostatin for heparin is explained by the presence of an extensive basic patch formed by 11 arginine residues. Endostatin may inhibit angiogenesis by binding to the heparan sulphate proteoglycans involved in growth factor signalling.
Insights
Endostatin, a collagen fragment, inhibits blood vessel growth in tumors. Its crystal structure reveals how it binds heparin, potentially blocking growth factor signaling and halting cancer progression without resistance.
Area of Science:
- Molecular Biology
- Structural Biology
- Cancer Research
Background:
- Extracellular proteins can possess latent anti-angiogenic properties.
- Endostatin, derived from collagen XVIII, is a potent inhibitor of endothelial cell proliferation and angiogenesis.
- Endostatin therapy in experimental cancers induces tumor dormancy and avoids resistance.
Purpose of the Study:
- To express recombinant mouse endostatin.
- To determine the crystal structure of endostatin.
- To elucidate the structural basis for endostatin's interaction with heparin and its anti-angiogenic mechanism.
Main Methods:
- Expression of recombinant mouse endostatin.
- X-ray crystallography to determine the 3D structure at 1.5 Å resolution.
- Analysis of structural features, including surface charge distribution and homology to known protein domains.
Main Results:
- The crystal structure of endostatin revealed a compact fold with distant homology to C-type lectin and Link modules.
- A significant basic patch, comprising 11 arginine residues, was identified, explaining endostatin's high affinity for heparin.
- The structure suggests a mechanism where endostatin inhibits angiogenesis by binding to heparan sulfate proteoglycans.
Conclusions:
- Endostatin's structure provides insights into its potent anti-angiogenic activity.
- Heparin binding, mediated by a basic patch, is a key feature of endostatin.
- Endostatin likely inhibits angiogenesis by interfering with growth factor signaling pathways involving heparan sulfate proteoglycans.