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High-affinity and low-affinity calcium binding and stability of the multidomain extracellular 40-kDa basement membrane glycoprotein (BM-40/SPARC/osteonectin)

Maurer, P. and Mayer, U. and Bruch, M. and Jeno, P. and Mann, K. and Landwehr, R. and Engel, J. and Timpl, R.. (1992) High-affinity and low-affinity calcium binding and stability of the multidomain extracellular 40-kDa basement membrane glycoprotein (BM-40/SPARC/osteonectin). European journal of biochemistry, Vol. 205, H. 1. pp. 233-240.

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Official URL: http://edoc.unibas.ch/dok/A5258325

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Abstract

Reversible binding of calcium ions to a single high-affinity binding site in the 40-kDa basement membrane protein (BM-40) caused a 33% increase of alpha-helicity, an about 60% change in intrinsic fluorescence and a dramatic increase of the rate of cleavage by alpha-chymotrypsin. All these effects exhibited identical dependencies on calcium concentration from which a dissociation constant Kd = 0.6 microM was determined. Calcium release was accompanied by an increase of the frictional ratio in solution but not by denaturation which occurred at about equal guanidine.HCl concentration for both calcium-saturated and calcium-depleted protein (midpoint 1.5 M). The cleavage sites for alpha-chymotrypsin are located in or near to the EF-hand domain IV of calcium-depleted BM-40 (also known as SPARC, i.e. secreted protein acidic and rich in cysteine, and osteonectin). These and other data indicate that binding occurs in the EF-hand domain from which a large conformational change is transmitted. Low-affinity calcium-binding sites in the N-terminal glutamic-acid-rich domain I of BM-40 were identified by human leukocyte elastase which was found to cleave very specifically in the middle of this domain. From the increase of cleavage rate with increasing calcium concentration a Kd greater than or equal to 10 mM was estimated. It is suggested that variations of calcium levels in the extracellular space in this range may regulate functions of BM-40 such as collagen binding and that high-affinity binding is important for stabilization, folding and secretion during biosynthesis.
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Services Biozentrum > Mass Spectrometry (Jenö)
UniBasel Contributors:Jenö, Paul
Item Type:Article, refereed
Article Subtype:Research Article
Bibsysno:Link to catalogue
Publisher:Blackwell
ISSN:0014-2956
Note:Publication type according to Uni Basel Research Database: Journal article
Last Modified:22 Mar 2012 14:20
Deposited On:22 Mar 2012 13:20

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