The roles of stoichiometric crowding and protein-protein interactions in accelerating translation elongation rates in E. coli

Translation elongation in Escherichia coli is a complex physico-chemical process, involving diffusive transport, entropic exclusion, and combinatoric matching between ribosomes and tRNAs. Previous work from our group has demonstrated that ‘stoichiometric crowding’ – the relative abundances and volume fractions of translation molecules – improves diffusive search times and drives an increase in ribosomal productivity as a function of cellular growth rate [Maheshwari et al., in review]. This physical phenomenon is insensitive to changes in chemical kinetics, though the overall elongation rate is underpredicted. Here, we extend our representative E. coli cytoplasm by incorporating attractions between EF-Tu–GFP–tRNA and ribosomal L7/L12 subunits, which are hypothesized to ‘pre-load’ ternary complexes onto ribosomes. We demonstrate the structural and dynamic implications of pre-loading, which ultimately combines with stoichiometric crowding to facilitate faster translation elongation rates.