Talk abstracts

Talk on Wednesday 04:00-04:15pm submitted by Qi Liu

Role of inter-subunit bridges in ribosomal translocation

Qi Liu (OSBP, The Ohio State University), Kurt Fredrick (OSBP, Department of Microbiology, The Ohio State University)

Abstract:
During each elongation cycle of translation, the ribosomal complex moves 3 nucleotides along the mRNA, a process termed translocation and catalyzed by Elongation Factor-G (EF-G). The work from Wintermeyer and coworkers has shown that the rate of translocation is limited by a conformational change of the ribosome, termed unlocking. 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 suggest that interactions between the subunits may be altered during unlocking. To systematically investigate the roles of individual inter-subunit bridges in translocation, we targeted most bridges by mutagenesis and characterized their effects on both EF-G-catalyzed forward and spontaneous reverse translocation. Mutations that disrupt bridge B1a and B4 showed significant acceleration of both forward and reverse translocation. These bridges are predicted to constrain 30S head swiveling and inter-subunit rotation respectively. These data provide evidence that both 30S head swiveling and inter-subunit rotation are part of the rate-limiting unlocking step of translocation.

Keywords: Ribosome, Translocation, Inter-subunit Bridge