# Determination of the structure of the recombinant T = 1 capsid of Sesbania mosaic virus

Sangita, V and Parthasarathy, S and Toma, S and Lokesh, GL and Gowri, TDS and Satheshkumar, PS and Savithri, HS and Murthy, MRN (2002) Determination of the structure of the recombinant T = 1 capsid of Sesbania mosaic virus. In: Current Science, 82 (9). pp. 1123-1131.

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The recombinant coat protein (CP) of Sesbania mosaic virus lacking segments of different lengths from the N-terminus expressed in E. coli was shown to selfassemble into a variety of distinct capsids encapsidating 23S rRNA from the host and CP mRNA in vivo.Particles with 60 copies (T = 1) of protein subunits were observed when protein lacking 65 amino acids from the N-terminus was expressed. This recombinant protein possesses the sequence corresponding to the S-domain of the native, T = 3 icosahedral particles but lacks the $\beta$-annulus, the $\beta$A strand (residues 67–70) and the arginine-rich ARM motif (residues 28–36). Purified T = 1 particles crystallized in the monoclinic space group $P2_1$ with cell parameters of a = 188.4 $\AA$, b = 194.6 $\AA$, c = 272.1 $\AA$ and $\beta$ = $92.6^°$. The structure of the T = 1 particles was determined by X-ray diffraction at 3.0 $\AA$ resolution. As expected, the poly-peptide fold of the subunit closely resembles that of the S-domain of the native virus. The recombinant particles bind calcium ions in a manner indistinguishable from that of the native capsids. The structure reveals the major differences in the quaternary organization responsible for the formation of T = 1 against T = 3 particles.