Ilag L L, McKenna R, Yadav M P, BeMiller J N, Incardona N L, Rossmann M G
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392.
J Mol Biol. 1994 Dec 2;244(3):291-300. doi: 10.1006/jmbi.1994.1730.
Monoclinic P2(1) crystals of the bacteriophage phi X174 have been incubated with calcium ions (Ca2+) and the induced structural conformational changes studied to 3 A resolution with X-ray crystallographic methods. Three different types of Ca2+ binding sites have been located within the asymmetric unit of the virion. Two sets of sites are associated with the F capsid protein. One set of sites associated with the F protein is in a general position near the icosahedral 3-fold axes of the virus, with the main-chain carbonyl oxygen atoms of residues Gly1321, Asp1421, Met1424 and Ser1426, and the side-chains of Gln1004 and Asp1421 as ligands. The other set of sites associated with the F protein is on the icosahedral 3-fold axes, with the symmetry-related main-chain carbonyl oxygen atoms of Ser1001 and the side-chains of Asn1002 as ligands. The bound Ca2+ induce a conformational change of the amino-terminal residues of the F proteins. A third set of sites, consisting of a pair of Ca2+ on the icosahedral 5-fold axes, are associated with the G spike protein and are concurrently liganded by the symmetry-related carbonyl oxygen side-chains of Asp2117. Concomitant with the binding of Ca2+ to the phage is the rotation of the Asp1209 side-chain of the F protein towards some additional electron density that was not observed in the absence of Ca2+. This density is situated in a shallow depression near the icosahedral 2-fold axes of the virus, and has been tentatively interpreted as a bound glucose molecule that is ordered only in the presence of Ca2+. The putative glucose binding site may be related to the attachment of the virus to cell surface lipopolysaccharides in the initial stages of Escherichia coli infection.
已将噬菌体φX174的单斜晶系P2(1)晶体与钙离子（Ca2+）一起孵育，并用X射线晶体学方法研究了诱导的结构构象变化，分辨率达到3埃。在病毒粒子的不对称单元内定位了三种不同类型的Ca2+结合位点。两组位点与F衣壳蛋白相关。与F蛋白相关的一组位点位于病毒二十面体3重轴附近的一般位置，以Gly1321、Asp1421、Met1424和Ser1426残基的主链羰基氧原子以及Gln1004和Asp1421的侧链作为配体。与F蛋白相关的另一组位点位于二十面体3重轴上，以Ser1001的对称相关主链羰基氧原子和Asn1002的侧链作为配体。结合的Ca2+诱导F蛋白氨基末端残基的构象变化。第三组位点由位于二十面体5重轴上的一对Ca2+组成，与G刺突蛋白相关，并同时由Asp2117的对称相关羰基氧侧链配位。与Ca2+结合到噬菌体同时发生的是F蛋白的Asp1209侧链向一些在没有Ca2+时未观察到的额外电子密度旋转。这种密度位于病毒二十面体2重轴附近的浅凹陷处，并初步解释为仅在有Ca2+时才有序排列的结合葡萄糖分子。推测的葡萄糖结合位点可能与大肠杆菌感染初始阶段病毒与细胞表面脂多糖的附着有关。
