X-ray crystal structure of bovine 3 Glu-osteocalcin.
X-ray crystal structure of bovine 3 Glu-osteocalcin.
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DOI：
10.1021/bi4010254
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发表时间：
2013-11-26
期刊：
影响因子：
2.9
通讯作者：
Dowd TL
中科院分区：
文献类型：
--
作者：
Malashkevich VN;Almo SC;Dowd TL
在低维生素K摄入或口服抗凝剂（华法林）期间，血清中骨钙素的3 Glu形式（3 Glu-OCN）增加。以前的报道使用圆二色性显示它的结构比3 Gla Ca ~（2+）-OCN少，并且不与骨矿物质强烈结合。最近的研究表明3 Glu-OCN作为一种潜在的葡萄糖代谢调节剂的作用。在胰腺和睾丸中发现的G蛋白偶联受体GPRC 6a被鉴定为推定的骨钙素受体。本研究的目的是确定高分辨率结构的牛3 Glu-OCN，使用X射线晶体学，了解分子与矿物质和GPRC 6a受体的相互作用。生长了热脱羧牛骨钙素的衍射质量晶体，并测定了晶体结构，分辨率为1.88 μ m。最终的精制结构包含残基17-47，并且与3 Gla Ca 2 +-OCN一样，由围绕疏水核心的三个α-螺旋组成，其中两个螺旋之间有一个C23-C29二硫键，并且没有结合的Ca 2+。因此，3 Glu-OCN的螺旋结构是不依赖于Ca 2+的，但类似于3 Gla Ca 2 +-OCN的螺旋结构。矿物质结合水平的降低可能是由于3 Glu-OCN上的Ca 2+配位体数量较少。该结构表明GPRC 6a受体可能对螺旋骨钙素有反应，并将有助于对3 Glu-OCN在葡萄糖稳态中的作用提供分子机制的见解。
The 3 Glu form of osteocalcin (3 Glu-OCN) is increased in serum during low vitamin K intake or oral anticoagulant use (warfarin). Previous reports using circular dichroism show it is less structured than 3 Gla Ca2+-osteocalcin and does not bind strongly to bone mineral. Recent studies have suggested a role for 3 Glu-OCN as a potential regulator of glucose metabolism. A G-protein-coupled receptor, GPRC6a, found in the pancreas and testes was identified as the putative osteocalcin receptor. The purpose of this study is to determine the high-resolution structure of bovine 3 Glu-OCN, using X-ray crystallography, to understand molecular interactions with mineral and the GPRC6a receptor. Diffraction quality crystals of thermally decarboxylated bovine osteocalcin were grown, and the crystal structure was determined to 1.88 Å resolution. The final refined structure contained residues 17–47 and, like 3 Gla Ca2+-OCN, consisted of three α-helices surrounding a hydrophobic core, a C23–C29 disulfide bond between two of the helices, and no bound Ca2+. Thus, the helical structure of 3 Glu-OCN is Ca2+-independent but similar to that of 3 Gla Ca2+-OCN. A reduced level of mineral binding could result from a lower number of Ca2+ coordinating ligands on 3 Glu-OCN. The structure suggests the GPRC6a receptor may respond to helical osteocalcin and will aid in providing molecular mechanistic insight into the role of 3 Glu-OCN in glucose homeostasis.