Crystal structure of human chondroadherin: Solving a difficult molecular-replacement problem using de novo models

Research output: Contribution to journalArticle

Abstract

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.The structure of human chondroadherin (hCHAD), a 359-amino-acid protein with 11 leucine-rich repeats, has been solved by molecular replacement using de novo models of a 195-residue segment and the AMPLE pipeline. This demonstrates that even a fairly large β-rich protein is tractable to solution using de novo modelling. The structure of the C-terminal domain of hCHAD reveals the conformation of a medically relevant peptide.

Details

Authors
Organisations
External organisations
  • Scripps Research Institute
  • Euro Diagnostica AB
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Structural Biology

Keywords

  • chondroadherin, collagen binding, de novo models, extracellular matrix, integrin binding, molecular replacement, small leucine-rich repeat proteins, structure prediction
Original languageEnglish
Pages (from-to)53-63
Number of pages11
JournalActa Crystallographica Section D: Structural Biology
Volume73
Issue number1
Publication statusPublished - 2017 Jan 1
Publication categoryResearch
Peer-reviewedYes