Bullock T L, Roberts T M, Stewart M
MRC Laboratory of Molecular Biology, Cambridge, England.
J Mol Biol. 1996 Oct 25;263(2):284-96. doi: 10.1006/jmbi.1996.0575.
We have determined the structure of the Ascaris major sperm protein (MSP) to 2.5 A resolution using X-ray crystallography. The MSP polypeptide chain has an immunoglobulin-like fold based on a seven-stranded beta sandwich. In two strands, cis-proline residues impart distinctive kinks, and overall the structure most closely resembles that of the N-terminal domain of the bacterial chaperonin, PapD. In the C2 crystal form which we have solved here, two MSP chains are tightly associated in the asymmetric unit and are related by a non-crystallographic 2-fold rotation axis. This arrangement almost certainly represents the MSP dimer that is present in solution. Additionally, the arrangement of two MSP dimers at one of the crystallographic 2-fold axes in the 215 A unit cell suggests a possible mode for the assembly of MSP into the filaments which promote cell movement. This dimer-dimer association is based on a beta sheet extension mechanism between adjoining MSP monomers which resembles the interaction between PapD and its protein substrate.
我们利用X射线晶体学技术，将蛔虫主要精子蛋白（MSP）的结构解析到了2.5埃的分辨率。MSP多肽链基于一个七链β折叠片层具有免疫球蛋白样折叠结构。在两条链中，顺式脯氨酸残基产生独特的弯折，总体而言，该结构与细菌伴侣蛋白PapD的N端结构域最为相似。在我们解析的C2晶体形式中，两条MSP链在不对称单元中紧密结合，并通过一个非晶体学的二重旋转轴相关联。这种排列几乎肯定代表了溶液中存在的MSP二聚体。此外，在215埃晶胞中一个晶体学二重轴处两个MSP二聚体的排列，提示了MSP组装成促进细胞运动的细丝的一种可能模式。这种二聚体-二聚体缔合基于相邻MSP单体之间的β折叠片层延伸机制，类似于PapD与其蛋白质底物之间的相互作用。
