EF-P is an essential protein that in eubacteria stimulates the formation of the first peptide bonds in protein synthesis. Studies show that EF-P prevents ribosomes from stalling during the synthesis of proteins containing consecutive prolines. EF-P binds to a site located between the binding site for the peptidyl tRNA and the exiting tRNA. It spans both ribosomal subunits with its amino-terminal domain positioned adjacent to the aminoacyl acceptor stem and its carboxyl-terminal domain positioned next to the anticodon stem-loop of the P site-bound initiator tRNA. The EF-P protein shape and size is very similar to a tRNA and interacts with the ribosome via the exit “E” site on the 30S subunit and the peptidyl-transferase center of the 50S subunit. EF-P is a translation aspect of an unknown function, therefore It probably functions indirectly by altering the affinity of the ribosome for aminoacyl-tRNA, thus increasing their reactivity as acceptors for peptidyl transferase. EF-P consists of three domains:
An N-terminal KOW-like domain
A central OB domain, which forms an oligonucleotide-binding fold. It is not clear if this region is involved in bindingnucleic acids
A C-terminal domain which adopts an OB-fold, with five beta-strands forming a beta-barrel in a Greek-key topology
Eukaryotes and archaebacteria lack EF-P. In eukaryotes, a similar function is performed by the eukaryotic initiation factor, eIF-5A, which exhibits some modest sequence and structural similarity with EF-P.. There are, however, many difference differences between EF-p and eIF-5A. EF-P has a structure similar to that of L-shaped tRNA and it contains three β-barrel domains. In contrast, eIF-5A contains only two domains. Moreover, as opposed to eIF-5A, which contains the non-proteinogenic amino acidhypusine that is essential for its activity, EF-P undergoes no post-translational amino acid modifications. Finally EF-P is about 40 amino acids longer than shorter than eIF-5A.
Function
In eubacteria, there are three groups of factors that promote protein synthesis: initiation factors, elongation factors and termination factors. The elongation phase of translation is promoted by three universal elongation factors, EF-Tu, EF-Ts, and EF-G. EF-P was discoverd in 1975 by Glick and Ganoza, as a factor that increased the yield of peptide bond formation between initiator fMet-tRNAfMet and a mimic of aa-tRNA, puromycin. The low yield of product formation in absence of EF-P can be described by the loss of peptidyl-tRNA from the stalled ribosome. Thus, EF-P is not a necessary component of minimal in vitro of translation system, however, the absence of EF-P can limit translation rate, increase antibiotic sensitivity, and slow growth. To complete its function, EF-P enters paused ribosomes through the E-site and facilitates peptide bond formation through interactions with the P-site tRNA. EF-P and eIF-5A both are essential for the synthesis of a subset of proteins containing proline stretches in all cells. It has been suggested that after binding of the initiator tRNA to the P/I site, it is correctly positioned to the P site by binding of EF-P to the E site. Additionally, EF-P has been shown to assist in efficient translation of three or more consecutive proline residues.
Structure
EF-P is a 21 kDa protein encoded by the efp gene. EF-P consists of three β-barrel domains and has a L shape tRNA structure. Domain II and III of EF-P are similar to each other. Despite the structural similarity of EF-P with tRNA, studies showed that, EF-P does not bind to the ribosome at the classical tRNA binding site, but at the distinct position that is located between the P and E sites.
