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NMR studies of the structure and Mg2+ binding properties of a conserved RNA motif of EMCV picornavirus IRES element.

ABSTRACT: The structure and Mg(2+) binding properties of a conserved 75mer RNA motif of the internal ribosome entry site (IRES) element of encephalomyocarditis virus picornavirus have been investigated by (1)H-NMR and UV melting experiments. The assignment of the imino proton resonances with characteristic chemical shift dispersion for canonical and non-canonical base pairs confirmed the predicted secondary structure of the 75mer and its fragments. Addition of Mg(2+) resulted in a dramatic increase in apparent melting temperature, with the 75mer RNA registering the biggest increase, from 63 to 80 degrees C, thus providing evidence for enhanced stability arising from Mg(2+) binding. Similarly, addition of Mg(2+) induced selective changes to the chemical shifts of the imino protons of a GCGA tetraloop in the 75mer, that is essential for IRES activity, thereby highlighting a possible structural role for Mg(2+) in the folding of the 75mer. Significantly, the same protons show retarded exchange to water solvent, even at elevated temperature, which suggest that Mg(2+) induces a conformational rearrangement of the 75mer. Thus, we propose that Mg(2+) serves two important roles: (i) enhancing thermodynamic stability of the 75mer RNA (and its submotifs) via non-specific interactions with the phosphate backbone and (ii) promoting the folding of the 75mer RNA by binding to the GCGA tetraloop.

SUBMITTER: Phelan M

PROVIDER: S-EPMC519103 | biostudies-literature | 2004

REPOSITORIES: biostudies-literature

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NMR studies of the structure and Mg2+ binding properties of a conserved RNA motif of EMCV picornavirus IRES element.

Phelan Marie M Banks Ryan J RJ Conn Graeme G Ramesh Vasudevan V

Nucleic acids research 20040907 16

The structure and Mg(2+) binding properties of a conserved 75mer RNA motif of the internal ribosome entry site (IRES) element of encephalomyocarditis virus picornavirus have been investigated by (1)H-NMR and UV melting experiments. The assignment of the imino proton resonances with characteristic chemical shift dispersion for canonical and non-canonical base pairs confirmed the predicted secondary structure of the 75mer and its fragments. Addition of Mg(2+) resulted in a dramatic increase in app ...[more]

PMID: 15353559

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Project description:Many picornaviruses cause important diseases in humans and other animals including poliovirus, rhinoviruses (causing the common cold) and foot-and-mouth disease virus (FMDV). These small, non-enveloped viruses comprise a positive-stranded RNA genome (ca. 7-9 kb) enclosed within a protein shell composed of 60 copies of three or four different capsid proteins. For the aphthoviruses (e.g. FMDV) and cardioviruses, the capsid precursor, P1-2A, is cleaved by the 3C protease (3Cpro) to generate VP0, VP3 and VP1 plus 2A. For enteroviruses, e.g. poliovirus, the capsid precursor is P1 alone, which is cleaved by the 3CD protease to generate just VP0, VP3 and VP1. The sequences required for correct processing of the FMDV capsid protein precursor in mammalian cells were analyzed. Truncation of the P1-2A precursor from its C-terminus showed that loss of the 2A peptide (18 residues long) and 27 residues from the C-terminus of VP1 (211 residues long) resulted in a precursor that cannot be processed by 3Cpro although it still contained two unmodified internal cleavage sites (VP0/VP3 and VP3/VP1 junctions). Furthermore, introduction of small deletions within P1-2A identified residues 185-190 within VP1 as being required for 3Cpro-mediated processing and for optimal accumulation of the precursor. Within this C-terminal region of VP1, five of these residues (YCPRP), are very highly conserved in all FMDVs and are also conserved amongst other picornaviruses. Mutant FMDV P1-2A precursors with single amino acid substitutions within this motif were highly resistant to cleavage at internal junctions. Such substitutions also abrogated virus infectivity. These results can explain earlier observations that loss of the C-terminus (including the conserved motif) from the poliovirus capsid precursor conferred resistance to processing. Thus, this motif seems essential for maintaining the correct structure of picornavirus capsid precursors prior to processing and subsequent capsid assembly; it may represent a site that interacts with cellular chaperones.

Dataset Information

NMR studies of the structure and Mg2+ binding properties of a conserved RNA motif of EMCV picornavirus IRES element.

Publications

NMR studies of the structure and Mg2+ binding properties of a conserved RNA motif of EMCV picornavirus IRES element.

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