Asporin competes with decorin for collagen binding, binds calcium and promotes osteoblast collagen mineralization

TY - JOUR

T1 - Asporin competes with decorin for collagen binding, binds calcium and promotes osteoblast collagen mineralization

AU - Kalamajski, Sebastian

AU - Aspberg, Anders

AU - Lindblom, Karin

AU - Heinegård, Dick

AU - Oldberg, Ake

N1 - Keywords: Amino Acid Sequence; Binding, Competitive; Calcification, Physiologic; Calcium; Cells, Cultured; Collagen; Cysteine; Disulfides; Extracellular Matrix Proteins; Fibrillar Collagens; Humans; Osteoblasts; Protein Binding; Proteoglycans

PY - 2009

Y1 - 2009

N2 - The interactions of the ECM (extracellular matrix) protein asporin with ECM components have previously not been investigated. Here, we show that asporin binds collagen type I. This binding is inhibited by recombinant asporin fragment LRR (leucine-rich repeat) 10-12 and by full-length decorin, but not by biglycan. We demonstrate that the polyaspartate domain binds calcium and regulates hydroxyapatite formation in vitro. In the presence of asporin, the number of collagen nodules, and mRNA of osteoblastic markers Osterix and Runx2, were increased. Moreover, decorin or the collagen-binding asporin fragment LRR 10-12 inhibited the pro-osteoblastic activity of full-length asporin. Our results suggest that asporin and decorin compete for binding to collagen and that the polyaspartate in asporin directly regulates collagen mineralization. Therefore asporin has a role in osteoblast-driven collagen biomineralization activity. We also show that asporin can be expressed in Escherichia coli (Rosetta-gami) with correctly positioned cysteine bridges, and a similar system can possibly be used for the expression of other SLRPs (small LRR proteoglycans/proteins).

AB - The interactions of the ECM (extracellular matrix) protein asporin with ECM components have previously not been investigated. Here, we show that asporin binds collagen type I. This binding is inhibited by recombinant asporin fragment LRR (leucine-rich repeat) 10-12 and by full-length decorin, but not by biglycan. We demonstrate that the polyaspartate domain binds calcium and regulates hydroxyapatite formation in vitro. In the presence of asporin, the number of collagen nodules, and mRNA of osteoblastic markers Osterix and Runx2, were increased. Moreover, decorin or the collagen-binding asporin fragment LRR 10-12 inhibited the pro-osteoblastic activity of full-length asporin. Our results suggest that asporin and decorin compete for binding to collagen and that the polyaspartate in asporin directly regulates collagen mineralization. Therefore asporin has a role in osteoblast-driven collagen biomineralization activity. We also show that asporin can be expressed in Escherichia coli (Rosetta-gami) with correctly positioned cysteine bridges, and a similar system can possibly be used for the expression of other SLRPs (small LRR proteoglycans/proteins).

U2 - 10.1042/BJ20090542

DO - 10.1042/BJ20090542

M3 - Journal article

C2 - 19589127

SN - 0264-6021

VL - 423

SP - 53

EP - 59

JO - Biochemical Journal

JF - Biochemical Journal

IS - 1

ER -