HOW DO TRANSLATION FACTORS CATALYSE PROTEIN SYNTHESIS?

Anders Liljas

Molecular Biophysics, Lund University, Lund, Sweden (anders.liljas@mbfys.lu.se)

tRNA is the adaptor in protein synthesis. The ribosome has three binding sites for tRNA, the A-, P-, and E-sites. The tRNAs bridge between the ribosomal subunits with the decoding site and the mRNA on the 30S subunit and the peptidyl transfer site on the 50S subunit.

Translation factors are needed to obtain the rate and fidelity required for protein synthesis. They catalyse protein synthesis on the ribosome. Several of the translation factors are GTPases and are structurally and functionally related. They catalyse irreversible steps in the process. Other translation factors operate in conjunction with the GTPases. Several of them bind to the tRNA binding sites on the ribosome and some of them are also tRNA mimics. Some of these tRNA mimics are EF-G, EF-P, SelB, RF1, RF2 and RRF. The range of tRNA mimicking proteins suggest that the shape similarity is not a sufficient criterion for binding to a tRNA binding site. Despite a tRNA similarity some factors bind differently to the ribosome from the tRNAs.

The GTP hydrolysis of the translational GTPases leads to an irreversible step forward in the translation process. The GTPasesare normally inactive enzymes, but at suitable states the ribosome activates their inherent capacity to hydrolyse GTP. This is done by a protein complex (L10*L12₄) whose structure and function is slowly becoming understood.