# Role of Metal Ion-mediated Interactions in the Assembly and Stability of Sesbania Mosaic Virus T=3 and T=1 Capsids

Satheshkumar, PS and Lokesh, GL and Sangita, V and Saravanan, V and Vijay, CS and Murthy, MRN and Savithri, HS (2004) Role of Metal Ion-mediated Interactions in the Assembly and Stability of Sesbania Mosaic Virus T=3 and T=1 Capsids. In: Journal of Molecular Biology, 342 (3). pp. 1001-1014.

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## Abstract

Sesbania mosaic virus (SeMV) capsids are stabilized by RNA–protein, protein–protein and calcium-mediated protein–protein interactions. The removal of calcium has been proposed to be a prerequisite for the disassembly of the virus. The crystal structure of native T=3 SeMV capsid revealed that residues D146 and D149 from one subunit and Y205, N267 and N268 of the neighboring subunit form the calcium-binding site (CBS).The CBS environment is found to be identical even in the recombinant CP-N$\Delta$65 T=1 capsids. Here, we have addressed the role of calcium and the residues involved in calcium co-ordination in the assembly and stability of T=3 and T=1 capsids by mutational analysis. Deletion of N267 and N268 did not affect T=3 or T=1 assembly, although the capsids were devoid of calcium, suggesting that assembly does not require calcium ions. However, the stability of the capsids was reduced drastically. Site-directed mutagenesis revealed that either a single mutation (D149N) or a double mutation (D146N-D149N) of SeMV coat protein affected drastically both the assembly and stability of T=3 capsids. On the other hand, the D146ND149N mutation in CP-N$\Delta$65 did not affect the assembly of T=1 capsid, although their stability was reduced considerably. Since the major difference between the TZ3 and T=1 capsids is the absence of the N-terminal arginine-rich motif (N-ARM) and the $\beta$-annulus from the subunits forming the T=1 capsids, it is possible that D149 initiates the N-ARM–RNA interactions that lead to the formation of the $\beta$-annulus, which is essential for T=3 capsid assembly.

Item Type: Journal Article The copyright of this article belongs to Elsevier. Sesbania mosaic virus;Calcium ions;Capsid assembly and stability Division of Biological Sciences > Molecular Biophysics UnitDivision of Biological Sciences > Biochemistry 12 Apr 2006 19 Sep 2010 04:25 http://eprints.iisc.ernet.in/id/eprint/6249