Crystal Structure Analysis of Spherical Viruses

TNV亚基由275个氨基酸组成。TNV晶体属于立方空间群P4_232，晶胞尺寸a=B=c=338*。对于3.86 × 10^7 *^3的单位细胞，包含两个分子量约为6.7 × 10^6的病毒颗粒，Vm值为2.9*^3/道尔顿。在100* 到5* 分辨率范围内，观察到的F>3sigma（F）的反射数为理论值的83%。C-亚基的N-末端臂（β A臂）的23个残基表现出有序结构。它比SBMV短3个残基。亚基A和B的相应主链段与SBMV中的那些一样是无序的。C亚基模型在对应于A亚基和B亚基的电子密度笼上进行假3倍旋转后很好地叠加，除了残基66至88的β A臂。二级结构沿多肽链命名为β A、β B、β C、α A、β D、β E、α B、β F、α C、β G、α D、α E、β H和β I沿着多肽链命名。A和B亚基在二十面体表面各有186个有序残基，TNV和SBMV亚基的三级结构比较表明，TNV亚基在α C和β G之间的环区有两个缺口，在α D和α E的连续片段中有五个缺口，在betaH和betaI之间的环中有两个缺口。alphaC和betaG之间的缺口位于病毒衣壳内部，其他缺口位于病毒颗粒的表面。TNV亚基C的有序β A臂比SBMV短三个残基。

The TNV subunit is composed of 275 amino acids. TNV crystals belong to the cubic space group P4_232 with the cell dimensions, a=b=c=338*. For the unit cell of 3.86x10^7*^3, containing two virus particles with a molecular weight of about 6.7x10^6, the Vm value is 2.9*^3/dalton. The observed reflections with F>3sigma (F) amounted to 83% of the theoretical number in the 100* to 5* resolution range.Electron density cages of the final map were constructed at 5* resolution. Twenty-three residues of an N-terminal arm (betaA arm) of the C-subunit exhibits ordered structure. It is shorter than that of SBMV by three residues. The corresponding main chain segments of the subunits A and B were disordered as those in SBMV.The C-subunit model was superposed well after pseudo 3-fold rotations on electron density cages corresponding to the A- and B-subunits except for the betaA arm from residues 66 to 88. Backbone structures around gaps in primary structure are superposed well on the electron density cages.Secondary structures were named betaA,betaB,betaC,alphaA,betaD,betaE,alphaB,betaF,alphaC,betaG,alphaD,alphaE,betaH and betaI along the polypeptide chain, following the nomenclature for SBMV.Each of A and B subunits has 186 ordered residues in the icosahedral surface, and C subunit has 24 additional ordered residues at betaA.Tertiary structural comparison between TNV and SBMV subunits shows that TNV subunits have two gaps in a loop region between alphaC and betaG,five gaps in continuous segments of alphaD and alphaE,and two gaps in a loop between betaH and betaI.The gaps between alphaC and betaG are inside the virus capsid, and the other gaps are on the surface of the virus particle. The ordered betaA arm of subunit C of TNV is shorter than that of SBMV by three residues.