NMR study of the interaction between PABP and the translation down-regulator Paip2

The poly(A) binding protein (PABP) is an essential translation factor that enhances protein synthesis and protects mRNAs from degradation. PABP is composed of four RNA recognition motifs (RRM) at its N-terminal and a peptide-interacting C-terminal domain. PABP-interacting proteins 1 (Paip1) and 2 (Paip2) were found to respectively stimulate or inhibit translation. Both Paip 1 and 2 contain two PABP interacting regions (PAM1 and PAM2). In this study, NMR was used to elucidate the mechanism by which Paip2 down-regulates translation through disruption of PABP's binding to poly(A) RNA. A fragment consisting of PABP RRM 2 and 3 was isotopically labeled and backbone NMR assignments were determined. From NMR titration with PABP RRM2-3 and the Paip2 PAM1 region, we determined that Paip2 binds in a positively charged cleft on the beta-sheet surface of RRM2-3 which is evolutionarily conserved. These results suggest a mechanism of how Paip2 displaces the mRNAs from PABP leading to translation inhibition