Horizontal gene transfer of a key translation protein has shaped the polyproline proteome

Prolines take longer than other amino acids to be incorporated into nascent proteins and cause ribosomes to stall during translation. This phenomenon occurs in all domains of life and is exacerbated at polyproline motifs. Such stalling can be eased by elongation factor P (EFP) in bacteria. We discovered a potential connection between horizontally transferred EFP variants and genomic signs of EFP dysfunction. Horizontal transfer of the efp gene has occurred several times throughout the bacterial tree of life, and such transfer events are associated with the loss of otherwise highly conserved polyproline motifs. In this study, we pinpoint cases of horizontal EFP transfer among a diverse set of bacterial genomes and examine the consequences of these events on genome evolution in the phyla Thermotogota and Planctomycetes. In these phyla, horizontal EFP transfer is not only associated with the loss of conserved polyproline motifs, but also with the loss of entire polyproline motif containing proteins, whose expression is likely dependent on EFP. In particular, three proteases (Lon, ClpC, and FtsH) and three tRNA synthetases (ValS, IleS1, IleS2) appear highly sensitive to EFP transfer. The conserved polyproline motifs within these proteins all reside within, or in close proximity to ATP binding regions, some of which have been shown to be crucial to their function. Our work shows that the horizontal transfer of EFP has left genomic traces that persist to this day. It also implies that the process of ‘domesticating’ a horizontally transferred efp gene can perturb the overall function of EFP.