title: Asporin competes with decorin for collagen binding, binds calcium and promotes osteoblast collagen mineralization.
abstract: 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).
authors: Department of Experimental Medical Science, University of Lund, Sweden. Sebastian.Kalamajski@childrens.harvard.edu
authors: Sebastian
authors: S
authors: Kalamajski
authors: Anders
authors: A
authors: Aspberg
authors: Karin
authors: K
authors: Lindblom
authors: Dick
authors: D
authors: Heinegård
authors: Ake
authors: A
authors: Oldberg
mesh_terms: D000595:Amino Acid Sequence; D001667:Binding, Competitive / Q000502:physiology; D002113:Calcification, Physiologic / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism; D058575:Decorin; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D024022:Fibrillar Collagens / Q000378:metabolism; D006801:Humans; D010006:Osteoblasts / Q000378:metabolism*; D011485:Protein Binding; D011509:Proteoglycans / Q000378:metabolism*
chemical_list: C439889:ASPN protein, human; C546878:DCN protein, human; D058575:Decorin; D004220:Disulfides; D016326:Extracellular Matrix Proteins; D024022:Fibrillar Collagens; D011509:Proteoglycans; D003094:Collagen; D003545:Cysteine; D002118:Calcium