Structural analysis of cooperative RNA binding by the La motif and central RRM domain of human La protein

Abstract

The La protein is a conserved component of eukaryotic ribonucleoprotein complexes that binds the 3' poly(U)-rich elements of nascent RNA polymerase III (pol III) transcripts to assist folding and maturation. This specific recognition is mediated by the N-terminal domain (NTD) of La, which comprises a La motif and an RNA recognition motif (RRM). We have determined the solution structures of both domains and show that the La motif adopts an alpha/beta fold that comprises a winged-helix motif elaborated by the insertion of three helices. Chemical shift mapping experiments show that these insertions are involved in RNA interactions. They further delineate a distinct surface patch on each domain-containing both basic and aromatic residues-that interacts with RNA and accounts for the cooperative binding of short oligonucleotides exhibited by the La NTD.

Roquin binding to target mRNAs involves a winged helix-turn-helix motif

“…Notably, no matches to other proteins with classical wHTH motifs and reported RNA-binding properties were found among the top hits in the structural similarity search 7 . However, to date only few such proteins have been described, displaying diverse RNA recognition modes [11][12][13][14][15][16] . Among these, the selenocysteine tRNA-specific elongation factor SelB is the single example of a wHTH-containing protein recognizing stem-loop mRNA.…”

NMR assignment of the N-terminal region of human La free and in complex with RNA

“…Expression and purification protocols of La NTD, encompassing residues 1-194, were carried out as reported previously (Alfano et al 2004). NMR samples contained 0.2-0.4 mM of doubly labelled apo protein in 20 mM TrisHCl, 100 mM KCl, 1 mM DTT, 10% D 2 O, pH 7.…”

“…NMR and X-ray revealed that the 3 0 -poly(U) recognition by La NTD is synergistically mediated by the La domain, an atypical member of the winged helix-turn-helix family, and the RRM; furthermore, this interaction involves structural motifs which are not the canonical nucleic acid binding surfaces in both classes of proteins, highlighting a novel mode of interaction with RNA ligands (Alfano et al 2004;Curry and Conte 2006;Teplova et al 2006).…”

Akt phosphorylation of La regulates specific mRNA translation in glial progenitors

“…La can shuttle between the nucleus and cytoplasm upon cellular stress (Baboonian et al, 1989;Bachmann et al, 1990). Cytoplasmic La promotes translation of a large variety of viral (Meerovitch et al, 1993;Chang et al, 1994) and cellular RNA (Kim et al, 2001;Holcik et al, 2003) through internal ribosome entry sites because of its modular structure (Trotta et al, 2003;Alfano et al, 2004;Dong et al, 2004). The fact that La is also able to facilitate translation of other mRNAs containing a 5 0 -UTR terminal oligopyrimidine element encoding ribosomal and translation relatedproteins (Crosio et al, 2000;Meyuhas, 2000;Cardinali et al, 2003) suggests a key role for La in mRNA translational regulation and makes La a potential candidate for the recruitment of oncogenic mRNAs to polysomes.…”