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Title
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Structure of a novel extracellular Ca(2+)-binding module in BM-40.
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Authors
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E.Hohenester,
P.Maurer,
C.Hohenadl,
R.Timpl,
J.N.Jansonius,
J.Engel.
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Ref.
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Nat Struct Biol, 1996,
3,
67-73.
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PubMed id
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Abstract
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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.
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