Protein-protein interactions facilitate transport of translation molecules in Escherichia coli: The roles of valency, affinity, and crowding

Faster growing cells must produce proteins more rapidly. Previous work from our group demonstrated that the mechanistic origin of this speedup in Escherichia coli is a coupled change in physical crowding and the molecular stoichiometry of translation molecules. Moreover, transport of these molecules dominates chemical reactions in setting how fast a cell can grow. Here, we extend our dynamic colloidal simulations to incorporate attractions between tRNA/GFP/EF-Tu ternary complexes and ribosomal L7/L12 subunits. We show that these interactions can organize the cytoplasm and facilitate transport, speeding up protein synthesis even further. However, the interaction valency - i.e., the number of ternary complexes that can bind to each ribosome - must be limited to recover in vivo measurements and prevent arrested phase separation of the cytoplasm.