Poster abstracts

Poster number 39 submitted by Qi Liu

The role of inter-subunit bridges in riboosmal translocation

Qi Liu (OSBP), Kurt Fredrick (Miocrobiology)

Abstract:
During each elongation cycle of translation, the ribosome moves 3 nucleotides along mRNA, a process termed translocation and normally catalyzed by Elongation Factor-G (EF-G). The rate of ribosomal translocation is limited by the unlocking step, a global conformational change of the ribosome (1). Despite its importance in protein synthesis, the nature of the unlocked state and the molecular mechanism of its formation remain unknown. Previous structural and biochemical studies indicated that some interactions between ribosome subunits, mediated by inter-subunit bridges, are altered during unlocking (2). To systematically investigate the role of individual inter-subunit bridges in ribosomal unlocking, we targeted various bridges by mutagenesis and characterized their effect on both EF-G catalyzed forward (3) and spontaneous reverse translocation (4). Our study identified several inter-subunit bridges important for translocation. Mutations that disrupt bridge B1a and B4, which locate on the outer edge of subunit interface, showed the most significant acceleration in both forward and reverse translocation. This result is in agreement with previous observation of the inter-subunit rotation of the ribosome by cryo-EM (5) and provides the first functional evidence to support that disruption of B1a and B4 are important for ribosomal unlocking.

References:
(1) Savelsbergh, A., Katunin, V. I., Mohr, D., Peske, F., Rodnina, M. V., Wintermeyer, W. (2003) Mol Cell 11, 1517-23.
(2) Yusupov, M. M., Yusupova, G. Z., Baucom, A., Lieberman, K., Earnest, T. N., Cate, J. H., Noller, H. F. (2001) Science 292, 883-896.
(3) Studer, S. M., Feinberg, J. S., Joseph S. J. (2003) Mol Biol 327, 369-381.
(4) Shoji, S., Walker, S. E., Fredrick, K. (2006) Mol Cell 24, 931-942.
(5) Valle, M., Zavialov, A., Sengupta, J., Rawat, U., Ehrenberg, M., Frank, J. (2003) Cell 114, 123-34.

Keywords: ribosome, translocation, inter-subunit bridge