W0180

The Structure of T=1 Icosahedral Particles Obtained from the Brome Mosaic Virus Coat Protein. Steven B. Larson, Robert W. Lucas, John S. Day, and Alexander McPherson, The Univ. of California, Irvine, CA 92697.

Brome Mosaic Virus (a T=3 icosahedral plant virus) disassembles when subjected to a high concentration of CaCl₂. The protein reassembles into T=1 icosahedral particles. SDS-PAGE and mass spectrometric molecular weight analyses of the T=1 proteins gave M_r = ~16,500 versus the native BMV protein with Mr = ~20,350. Amino terminal sequencing of the T=1 protein identified the cleavage point to be between residues 35 and 36.

The T=1 particles crystallize in the tetragonal space group P4₁22 with Z=4 and cell edges of a=b=193 and c=428 Å. Data were collected at the Advanced Light Source.

The structure was solved by molecular replacement by contracting a T=3 BMV pentamer along the 5 fold axis and rotating it about that axis while monitoring the correlation coefficient. The model that maximized the correlation coefficient was refined as a rigid body and subsequently used to determine initial phases for phase refinement and phase extension employing non-crystallographic symmetry.

The T=1 BMV particle has protruding pentamers with gaping holes at the three-fold axes. The structure of the protein, individually and as a pentamer unit, will be compared to those found in the native BMV virion.

Crystallization of Brome Mosaic Virus and T=1 Brome Mosaic Virus Particles Following a Structural Transition. R.W. Lucas, Y.G.Kuznetsov, S.B. Larson and A. McPherson, Virology 286, 290-303(2001). The Crystallographic Structure of Brome Mosaic Virus. R.W. Lucas, S.B. Larson and A. McPherson, J. Mol. Biol. 317, 95-108(2002).