Structure of a novel extracellular Ca(2+)-binding module in BM-40.
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Hohenester E, Maurer P, Hohenadl C, Timpl R, Jansonius JN, Engel J
Structure of a novel extracellular Ca(2+)-binding module in BM-40.
Nat Struct Biol. 1996 Jan;3(1):67-73.
- PubMed ID
- 8548457 [ View in PubMed]
- Abstract
The EF-hand is a highly conserved Ca(2+)-binding motif found in many cytosolic Ca(2+)-modulated proteins. Here we report the crystal structure at 2.0 A resolution of the carboxy-terminal domain of human BM-40 (SPARC, osteonectin), an extracellular matrix protein containing an EF-hand pair. The two EF-hands interact canonically but their detailed structures are unusual. In the first EF-hand a one-residue insertion is accommodated by a cis-peptide bond and by substituting a carboxylate by a peptide carbonyl as a Ca2+ ligand. The second EF-hand is stabilized by a disulphide bond. The EF-hand pair interacts tightly with an amphiphilic amino-terminal helix, reminiscent of target peptide binding by calmodulin. The present structure defines a novel protein module occurring in several other extracellular proteins.