Crystal structure of human chondroadherin: solving a difficult molecular-replacement problem using de novo models
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- 作者：Sebastian Rä ; misch ; Anna Pramhed ; Viveka Tillgren ; Anders Aspberg and Derek T. Logan
- 关键词：chondroadherin ; small leucine-rich repeat proteins ; extracellular matrix ; integrin binding ; collagen binding ; de novo models ; molecular replacement ; structure prediction
- 刊名：Acta Crystallographica Section D
- 出版年：2017
- 出版时间：January 2017
- 年：2017
- 卷：73
- 期：1
- 页码：53-63
- 全文大小：1513K
- ISSN：1399-0047
文摘
Chondroadherin (CHAD) is a cartilage matrix protein that mediates the adhesion of isolated chondrocytes. Its protein core is composed of 11 leucine-rich repeats (LRR) flanked by cysteine-rich domains. CHAD makes important interactions with collagen as well as with cell-surface heparin sulfate proteoglycans and α2β1 integrins. The integrin-binding site is located in a region of hitherto unknown structure at the C-terminal end of CHAD. Peptides based on the C-terminal human CHAD (hCHAD) sequence have shown therapeutic potential for treating osteoporosis. This article describes a still-unconventional structure solution by phasing with de novo models, the first of a β-rich protein. Structure determination of hCHAD using traditional, though nonsystematic, molecular replacement was unsuccessful in the hands of the authors, possibly owing to a combination of low sequence identity to other LRR proteins, four copies in the asymmetric unit and weak translational pseudosymmetry. However, it was possible to solve the structure by generating a large number of de novo models for the central LRR domain using Rosetta and multiple parallel molecular-replacement attempts using AMPLE. The hCHAD structure reveals an ordered C-terminal domain belonging to the LRRCT fold, with the integrin-binding motif (WLEAK) being part of a regular α-helix, and suggests ways in which experimental therapeutic peptides can be improved. The crystal structure itself and docking simulations further support that hCHAD dimers form in a similar manner to other matrix LRR proteins.