Wang Iren, Lou Yuan-Chao, Wu Kuen-Phon, Wu Shih-Hsiung, Chang Wen-Chang, Chen Chinpan
Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan, ROC.
J Mol Biol. 2005 Mar 4;346(4):1071-82. doi: 10.1016/j.jmb.2004.12.029. Epub 2005 Jan 16.
A number of beta-microseminoproteins (MSPs) have been identified from different species. MSPs are all non-glycosylated and disulfide bond-rich, but show a relatively low level of conservation. Although all Cys residues are conserved, our previous study showed that the disulfide bond pairings differ in porcine and ostrich MSPs. Despite the variety of biological functions that have been suggested for MSPs, their real function is still poorly understood. Furthermore, no 3D structure has been reported for any MSP, so the determination of the structure and function of MSPs is an interesting and important task. In the present study, we determined the 3D solution structure of porcine MSP on the basis of 1018 restraints. The ensemble of 20 NMR structures was well defined, with average root-mean-square deviations of 0.83(+/-0.16) A for the backbone atoms and 1.37(+/-0.17) A for heavy-atoms in residues 2-90. The 3D structure showed that porcine MSP is clearly composed of two domains, an N-terminal domain consisting of one double-stranded and one four-stranded antiparallel beta-sheet, and a C-terminal domain consisting of two double-stranded antiparallel beta-sheet. The orientation of the two domains was derived mainly on the basis of long-range NOEs and verified using residual dipolar coupling data. No inter-domain hydrophobic interaction or H-bonding was detected. However, a number of charged residues were found in close proximity between the domains, indicating that electrostatic interaction may be the key factor for the orientation of the two domains. This is the first report of a 3D structure for any MSP. In addition, structural comparison based on distance matrix alignment (DALI), class architecture topology and homologous superfamily (CATH) and combinatorial extension (CE) methods revealed that porcine MSP has a novel structure with a new fold providing valuable information for future structural studies on other MSPs and for understanding their biological functions.
已从不同物种中鉴定出多种β-微精蛋白（MSP）。MSP均为非糖基化且富含二硫键，但保守程度相对较低。尽管所有半胱氨酸残基都是保守的，但我们之前的研究表明，猪和鸵鸟MSP中的二硫键配对不同。尽管已有人提出MSP具有多种生物学功能，但其实际功能仍知之甚少。此外，尚未有任何MSP的三维结构报道，因此确定MSP的结构和功能是一项有趣且重要的任务。在本研究中，我们基于1018个约束条件确定了猪MSP的三维溶液结构。20个核磁共振结构的整体定义良好，残基2 - 90中主链原子的平均均方根偏差为0.83（±0.16）Å，重原子的平均均方根偏差为1.37（±0.17）Å。三维结构表明，猪MSP明显由两个结构域组成，一个N端结构域由一个双链和一个四链反平行β-折叠组成，一个C端结构域由两个双链反平行β-折叠组成。两个结构域的取向主要基于长程核Overhauser效应（NOE）推导得出，并使用残余偶极耦合数据进行了验证。未检测到结构域间的疏水相互作用或氢键。然而，在结构域之间发现了许多带电荷的残基紧密相邻，这表明静电相互作用可能是两个结构域取向的关键因素。这是关于任何MSP三维结构的首次报道。此外，基于距离矩阵比对（DALI）、类结构拓扑和同源超家族（CATH）以及组合扩展（CE）方法的结构比较表明，猪MSP具有一种新的结构和新的折叠方式，为未来对其他MSP的结构研究及其生物学功能的理解提供了有价值的信息。
