The protein-mineral interface in bone: a solid-state NMR study

Lead Research Organisation: University of Cambridge
Department Name: Chemistry

Abstract

Bone is a very important material in our bodies and those of other animals. It is known to consist of a matrix of protein (primarily, collagen) in which are embedded inorganic crystals of calcium phosphate. There is, at present, very little known about how the protein matrix and calcium phosphate crystals stick together, yet if they did not stick together in some way, the calcium phosphate crystals would all sink to the bottom of the bone and the bone would be floppy, and of very little use in supporting our bodies. The interface between the protein and calcium phosphate is thus of key importance in understanding how bone works as a material, how it is tough, and rigid enough to support our bodies and their movement, yet surprisingly resistant to fracture. We will use a measurement method called solid-state NMR to (a) identify which part of the protein matrix interacts with the calcium phosphate and (b) how far apart the matrix and crystals are. We will also look at how much force is required to break the link between the protein and calcium phosphate and see what effect diseases, such as osteoarthritis and osteoporosis have. The hope is that this will give clues as to how to treat these diseases as well as give us important information when building mathematical models to describe the functioning of bone as a material.

Technical Summary

Bone consists of a protein matrix (primarily collagen) in which are embedded crystals of a complex phase of calcium phosphate, dominated by hydroxyapatite. We will use solid-state NMR (primarily 31-P - 13-C REDOR) to identify the peptide groups in the matrix responsible for binding the matrix to the inorganic phase and to measure the distance of these groups from the crystal surfaces. The surface of the calcium phosphate crystals is known to be disordered, in common with the surface of most ionic crystals. We will use solid-state NMR to further characterise the structural units in the surface, via 31-P and 1-H NMR and various 2D correlation experiments. The work will use a variety of samples, including bone from animals of different ages and those suffering from osteoporosis and osteoarthritis, in order that we can determine the natural range of variation in the protein-mineral interface. In order to characterise the failure mode of the interface, and the stress required to disrupt it, samples will be mechanically impacted and re-examined by NMR.

Publications

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Duer M (2008) Mineral Surface in Calcified Plaque Is Like That of Bone Further Evidence for Regulated Mineralization in Arteriosclerosis, Thrombosis, and Vascular Biology

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Reid D.G. (2010) Kidney stone composition by solid state NMR (SSNMR) in European Cells and Materials

 
Description 1. Identification for the first time of the molecular species in bone matrix that binds to the mineral component. This project showed unequivocally that it is a chondroitin sulphate-like glycosaminoglycan (GAG), and significantly, not a protein which current opinion in bone biology (nor our original grant application!) expected.

2. Discovery that this molecular species performs the same role in other mineralised tissues, namely tooth enamel, calcified cartilage and mineralised atherosclerotic plaques.

3. Providing the first direct evidence that mineralisation of medial atherosclerotic plaques is a controlled process, much like the mineralisation process in bone.
Exploitation Route To understand how bone calcification may be impaired in disease and ageing; to understand pathological calcification in other tissues
Sectors Healthcare,Pharmaceuticals and Medical Biotechnology

URL http://www.ch.cam.ac.uk/person/mjd13
 
Description We have have used them to understand calcification in other tissues and have now shown that pathological vascular calcification proceeds by a very similar mechanism to the physiological process in bone. Ultimately, this will led to drugs that prevent vascular calcification
First Year Of Impact 2007
Sector Education,Pharmaceuticals and Medical Biotechnology
 
Description Atomic level structure of Extracellular Matrix (ECM): Spectroscopic approaches to the systems biology of intact tissue
Amount £594,448 (GBP)
Funding ID BB/G021392/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 10/2009 
End 03/2013