1nub
From Proteopedia
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HELIX C DELETION MUTANT OF BM-40 FS-EC DOMAIN PAIR
Overview
The extracellular calcium-binding domain (positions 138-286) of the matrix, protein BM-40 possesses a binding epitope of moderate affinity for several, collagen types. This epitope was predicted to reside in helix alphaA and, to be partially masked by helix alphaC. Here we show that deletion of, helix alphaC produces a 10-fold increase in collagen affinity similar to, that seen after proteolytic cleavage of this helix. The predicted removal, of the steric constraint was clearly demonstrated by the crystal structure, of the mutant at 2.8 A resolution. This constitutively activated mutant, was used to map the collagen-binding site following alanine mutagenesis at, 13 positions. Five residues were crucial for binding, R149 and N156 in, helix alphaA, and L242, M245 and E246 in a loop region connecting the two, EF hands of BM-40. These residues are spatially close and form a flat ring, of 15 A diameter which matches the diameter of a triple-helical collagen, domain. The mutations showed similar effects on binding to collagens I and, IV, indicating nearly identical binding sites on both collagens. Selected, mutations in the non-activated mutant DeltaI also reduced collagen, binding, consistent with the same location of the epitope but in a more, cryptic form in intact BM-40.
About this Structure
1NUB is a Single protein structure of sequence from Homo sapiens with CA as ligand. Full crystallographic information is available from OCA.
Reference
Crystal structure and mapping by site-directed mutagenesis of the collagen-binding epitope of an activated form of BM-40/SPARC/osteonectin., Sasaki T, Hohenester E, Gohring W, Timpl R, EMBO J. 1998 Mar 16;17(6):1625-34. PMID:9501084
Page seeded by OCA on Mon Nov 12 18:25:30 2007
