| Research Abstract |
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.
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