Role of the N-terminal region of ribosomal protein S7 in its interaction with 16S rRNA which binds to the concavity formed by the beta-ribbon arm and the alpha-helix

Eukaryotic Ribosomal Protein S5 of the 40S Subunit: Structure and Function

The ribosomal protein RPS5 is one of the prime proteins to combine with RNA and belongs to the conserved ribosomal protein family. It plays a substantial role in the process of translation and also has some non-ribosome functions. Despite the enormous studies on the relationship between the structure and function of prokaryotic RPS7, the structure and molecular details of the mechanism of eukaryotic RPS5 remain largely unexplored. This article focuses on the structure of RPS5 and its role in cells and diseases, especially the binding to 18S rRNA. The role of RPS5 in translation initiation and its potential use as targets for liver disease and cancer are discussed.

Deletion mutations in N-terminal alpha1 helix render heat labile enterotoxin B subunit susceptible to degradation

Heat-labile enterotoxin (LT) from enterotoxigenic Escherichia coli is a heterohexameric protein consisting of an enzymatically active A subunit, LTA, and a carrier pentameric B subunit, LTB. It is clear from the crystal structure of LTB that the N-terminal alpha1 helix lies outside the core structure. However, the function of the N-terminal alpha1 helix of LTB is unknown. The present work was carried out to investigate the effect of site-directed mutagenesis of the alpha1 helix on LTB synthesis. Six amino acids (PQSITE) located at positions 2-7 from the N terminus, including 4 aa from the alpha1 helix, were deleted by site-directed mutagenesis. The deletion resulted in complete inhibition of LTB expression in E. coli when expressed along with its signal sequence. A single amino acid deletion within the alpha1 helix also resulted in loss of expression. However, a single amino acid deletion outside the alpha1 helix did not affect LTB synthesis. Mutant proteins, whose synthesis was not detected in vivo, could be successfully translated in vitro by using the coupled transcription-translation system. Immunoblot analysis, Northern blot analysis, and in vitro transcription-translation data collectively indicate that the lack of synthesis of the mutant proteins is caused by the immediate degradation of the expressed product by cellular proteases rather than by faulty translation of mutant LTB mRNA. Coexpression of the LTA could not rescue the degradation of LTB mutants.

Crystal structure of the 30 S ribosomal subunit from Thermus thermophilus: structure of the proteins and their interactions with 16 S RNA

We present a detailed analysis of the protein structures in the 30 S ribosomal subunit from Thermus thermophilus, and their interactions with 16 S RNA based on a crystal structure at 3.05 A resolution. With 20 different polypeptide chains, the 30 S subunit adds significantly to our data base of RNA structure and protein-RNA interactions. In addition to globular domains, many of the proteins have long, extended regions, either in the termini or in internal loops, which make extensive contact to the RNA component and are involved in stabilizing RNA tertiary structure. Many ribosomal proteins share similar alpha+beta sandwich folds, but we show that the topology of this domain varies considerably, as do the ways in which the proteins interact with RNA. Analysis of the protein-RNA interactions in the context of ribosomal assembly shows that the primary binders are globular proteins that bind at RNA multihelix junctions, whereas proteins with long extensions assemble later. We attempt to correlate the structure with a large body of biochemical and genetic data on the 30 S subunit.

Ribosomal protein S7 from Escherichia coli uses the same determinants to bind 16S ribosomal RNA and its messenger RNA

Ribosomal protein S7 from Escherichia coli binds to the lower half of the 3' major domain of 16S rRNA and initiates its folding. It also binds to its own mRNA, the str mRNA, and represses its translation. Using filter binding assays, we show in this study that the same mutations that interfere with S7 binding to 16S rRNA also weaken its affinity for its mRNA. This suggests that the same protein regions are responsible for mRNA and rRNA binding affinities, and that S7 recognizes identical sequence elements within the two RNA targets, although they have dissimilar secondary structures. Overexpression of S7 is known to inhibit bacterial growth. This phenotypic growth defect was relieved in cells overexpressing S7 mutants that bind poorly the str mRNA, confirming that growth impairment is controlled by the binding of S7 to its mRNA. Interestingly, a mutant with a short deletion at the C-terminus of S7 was more detrimental to cell growth than wild-type S7. This suggests that the C-terminal portion of S7 plays an important role in ribosome function, which is perturbed by the deletion.