Decrypting the functional design of unmodified translation elongation factor P

Stalling of ribosomes due to consecutive proline motifs during polypeptide synthesis is a challenge faced by organisms across all kingdoms. To overcome this, bacteria employ translation elongation factor P (EF-P), while archaea and eukaryotes rely on a/eIF5A. Typically, these elongation factors become active only after undergoing post-translational modifications (PTMs) such as ß-lysinylation, (deoxy-)hypusinylation, rhamnosylation, or 5-aminopentanolyation. An exception to this rule is found in EF-P members of the PGKGP-subfamily, which remain unmodified. However, the mechanism behind the ability of certain bacteria to bypass metabolically and energetically costly PTMs, thus retaining active EF-P, remains unclear. In this study, we investigated the design principles governing the full functionality of unmodified EF-Ps in Escherichia coli. We first screened for naturally unmodified EF-Ps that are active in an E. coli reporter strain. We identified EF-P from Rhodomicrobium vannielii capable of rescuing the growth deficiencies and changes in the proteome of E. coli ΔepmA mutant lacking the gene for the modifying EF-P-(R)-ß-lysine ligase. We then identified specific amino acids in domain I of the unmodified EF-P variant that affected its activity. Ultimately, we transferred these functional properties to other marginally active members of the PGKGP EF-P subfamily, resulting in fully functional unmodified variants in E. coli. These results have not only implications for the improved heterologous expression of polyproline-containing proteins in E. coli but offer applications for other bacterial hosts. Understanding the mechanisms that underlie the functionality of unmodified EF-P provides insights into cellular adaptations to optimize protein synthesis.