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Structural Studies of MS2 Bacteriophage Virus Particle Disassembly by Nuclear Magnetic Resonance Relaxation Measurements

Centro Nacional de Ressonância Magnética Nuclear, Departamento de Bioquímica Médica, ICB, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; and ^* University of New Mexico School of Medicine and Cancer Research and Treatment Center, Albuquerque, New Mexico USA

Correspondence: Address reprint requests to A. P. Valente and F. C. L. Almeida, Universidade Federal do Rio de Janeiro, Av. Brig. Trompowiski, s/n Centro de Ciências da Saúde Bioco E Sala 10, Cidade Universitária, Rio de Janeiro, Brazil 21941-590. Tel.: 55-21-2-562-6756; Fax: 55-21-2-270-8647; E-mail: falmeida{at}cnrmn.bioqmed.ufrj.br.

In this article we studied, by nuclear magnetic resonance relaxation measurements, the disassembly of a virus particle—the MS2 bacteriophage. MS2 is one of the single-stranded RNA bacteriophages that infect Escherichia coli. At pH 4.5, the phage turns to a metastable state, as is indicated by an increase in the observed nuclear magnetic resonance signal intensity upon decreasing the pH from 7.0 to 4.5. Steady-state fluorescence and circular dichroism spectra at pH 4.5 show that the difference in conformation and secondary structure is not pronounced if compared with the phage at pH 7.0. At pH 4.5, two-dimensional ¹⁵N-¹H heteronuclear multiple quantum coherence (HMQC) spectrum shows 40 crosspeaks, corresponding to the most mobile residues of MS2 coat protein at pH 4.5. The ¹⁵N linewidth is 30 Hz, which is consistent with an intermediate with a rotational relaxation time of 100 ns. The average spin lattice relaxation time (T₁) of the mobile residues was measured at different temperatures, clearly distinguishing between the dimer and the equilibrium intermediate. The results show, for the first time, the presence of intermediates in the process of dissociation of the MS2 bacteriophage.