Talk abstracts

Talk on Saturday 09:40-10:00am submitted by Sanjaya Abeysirigunawardena

Studies on pH Dependence of the Escherichia coli 23 S rRNA Helix 69 Structure

Sanjaya C. Abeysirigunawardena (Department of Chemistry, Wayne State University), Christine S. Chow (Department of Chemistry, Wayne State University)

Abstract:
One region of the ribosome of high interest is helix 69 of 23S rRNA. Helix 69 of Escherichia coli (E. coli) 23S rRNA has three Ø residues at positions 1911, 1915 and 1917. The Ø residue at position 1915 is methylated. This helix resides at the interface of the large and small subunits of the ribosome. A large contact area of the ribosomal inter-subunit bridge B2a includes helix 69, for which the crystal structure shows slightly different conformations of the loop region.1 It is proposed that helix 69 is important for ribosomal release. Furthermore, it has been suggested that the binding of ribosomal recycling factor changes the conformation of the helix 69. Our work involves understanding the dynamic nature of helix 69 and contribution of pH to its structure. It is hypothesized that changes in pH may result in conformational changes of the helix 69 structure. Biophysical methods including circular dichroism spectroscopy, thermal melting analysis and NMR spectroscopy were used to explore the pH-dependent changes in helix 69 structure, and to determine if the pH effects are localized to specific microenvironments within helix 69 involving the modified nucleotides. Comparisons were made between the wild-type helix 69 and the unmodified helix 69 construct, in which pseudouridines and 3-methylpseudouridine were replaced by uridines. These comparisons emphasize the importance of the pseudouridine modification in structure and dynamics of helix 69.

References:
1. Schuwrith, B.S., Borovinskya, M.A., Hau, C.W., Zhang, W., Vila-Sanjurjo, A., Holton, J.M., and Cate, J.H.D. 2005. Structures of the bacterial ribosome at 3.5 Å resolution. Science 310: 827-834.

Keywords: Helix 69, Pseudouridine