Hohenester E, Maurer P, Hohenadl C, Timpl R, Jansonius J N, Engel J
Department of Structural Biology, University of Basel, Switzerland.
Nat Struct Biol. 1996 Jan;3(1):67-73. doi: 10.1038/nsb0196-67.
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.
EF 手型结构是一种在许多胞质 Ca(2+) 调节蛋白中发现的高度保守的 Ca(2+) 结合基序。在此，我们报告了人类 BM - 40（骨连接素、富含半胱氨酸的酸性分泌蛋白）羧基末端结构域的晶体结构，分辨率为 2.0 Å，BM - 40 是一种含有一对 EF 手型结构的细胞外基质蛋白。这两个 EF 手型结构典型地相互作用，但其详细结构却不寻常。在第一个 EF 手型结构中，一个单残基插入通过一个顺式肽键以及以肽羰基取代羧酸盐作为 Ca2+ 配体得以容纳。第二个 EF 手型结构通过一个二硫键得以稳定。这一对 EF 手型结构与一个两亲性氨基末端螺旋紧密相互作用，这让人联想到钙调蛋白与靶肽的结合方式。目前的结构定义了一种存在于其他几种细胞外蛋白中的新型蛋白质模块。
