Talk abstracts

Talk on Saturday 10:40-11:00am submitted by Xiaoyan Sun

NMR Characterization of Mg2+ Dependent Structural Plasticity in the Bulge

Xiaoyan Sun (Department of Chemistry & Biophysics Research Division, University of Michigan), Qi Zhang (Department of Chemistry & Biophysics Research Division, University of Michigan), Hashim M. Al-Hashimi (Department of Chemistry & Biophysics Research Division, University of Michigan)

Abstract:
SL-1 is a highly conserved stem-loop RNA element that plays an essential role in the dimerization and non-covalent attachment of two copies of the HIV viral genome which must be specifically packaged during viral assembly. The function of SL-1 is believed to involve a dynamical structural transition between metastable kissing and thermodynamically stable duplex forms of the SL1 dimer. This structural isomerization can occur spontaneously, has been shown to be dependent on the presence of a highly conserved SL-1 internal bulge and Mg2+ divalent cations, and is believed to be catalyzed in vivo by the nucleocapsid protein. Using NMR, including residual dipolar couplings and motionally decoupled relaxation data, we characterized the structural plasticity of the bulge-containing SL-1 monomer and its dependence on Mg2+ binding. We observe a combination of local and global nanosecond and micro-to-millsecond motions in free SL-1 that are arrested upon Mg2+ binding to the bulge. Our results rationalize in vitro studies on spontaneous structural isomerization including dependence on the presence/absence of the bulge and Mg2+ and suggest that the role of NcP in isomerization may involve the ejection of stabilizing Mg2+ ions that are bound at the guanine rich internal bulge.

Keywords: RNA dynamics, NMR, Mg effect