Protein synthesis elongation factor Tu present in spores of Streptomyces coelicolor can be phosphorylated in vitro by the spore protein kinase

Functions and Regulation of Translation Elongation Factors

Translation elongation is a key step of protein synthesis, during which the nascent polypeptide chain extends by one amino acid residue during one elongation cycle. More and more data revealed that the elongation is a key regulatory node for translational control in health and disease. During elongation, elongation factor Tu (EF-Tu, eEF1A in eukaryotes) is used to deliver aminoacyl-tRNA (aa-tRNA) to the A-site of the ribosome, and elongation factor G (EF-G, EF2 in eukaryotes and archaea) is used to facilitate the translocation of the tRNA₂-mRNA complex on the ribosome. Other elongation factors, such as EF-Ts/eEF1B, EF-P/eIF5A, EF4, eEF3, SelB/EFsec, TetO/Tet(M), RelA and BipA, have been found to affect the overall rate of elongation. Here, we made a systematic review on the canonical and non-canonical functions and regulation of these elongation factors. In particular, we discussed the close link between translational factors and human diseases, and clarified how post-translational modifications control the activity of translational factors in tumors.

First insights into salt tolerance improvement of Stevia by plant growth-promoting Streptomyces species

The present study aimed to investigate the potential of plant growth-promoting rhizobacteria (PGPR) to improve the salt stress and alleviate its impact on Stevia crop plant under different levels of salt concentration. Two Streptomyces spp. isolated from the rhizosphere of halophytic plants (Cucumis sativus L. and Salicornia europaea L.) have shown potential for plant growth promotion in Stevia plant. The streptomycetes isolates were identified by classical microbiological techniques and partial sequencing of 16S rRNA gene as Streptomyces variabilis (4NC) and S. fradiae (8PK). The results have shown that inoculation of Stevia plant by these isolates has enhanced plant growth parameters under applied salt stress. Moreover, total cellular proteins were extracted from the two Streptomyces isolates and SDS-PAGE technique was conducted. Mass spectrometric analysis has identified unique polypeptide of the elongation factor thermos unstable (EF-Tu) indicating the elevation of ribosomal RNA and ribosomal protein genes transcription. On the same context, alleviation of salt stress in Stevia plants inoculated with the two Streptomyces isolates has potentially promoted the accumulation of the major pronounced RuBisCO large subunit protein band detected approximately at 53 kDa. These results may give novel insights and accretion our understanding of salinity tolerance mechanisms using PGP streptomycetes to develop resistant sugar crops of highly important economic value. This study has presented the integration of microbiological, biochemical, and molecular techniques to evaluate the effect of salt stress and to assess the level of stress amelioration using PGPR on proteostasis of sugar crops in Egypt.

Phosphorylation decelerates conformational dynamics in bacterial translation elongation factors

Bacterial protein synthesis is intricately connected to metabolic rate. One of the ways in which bacteria respond to environmental stress is through posttranslational modifications of translation factors. Translation elongation factor Tu (EF-Tu) is methylated and phosphorylated in response to nutrient starvation upon entering stationary phase, and its phosphorylation is a crucial step in the pathway toward sporulation. We analyze how phosphorylation leads to inactivation of Escherichia coli EF-Tu. We provide structural and biophysical evidence that phosphorylation of EF-Tu at T382 acts as an efficient switch that turns off protein synthesis by decoupling nucleotide binding from the EF-Tu conformational cycle. Direct modifications of the EF-Tu switch I region or modifications in other regions stabilizing the β-hairpin state of switch I result in an effective allosteric trap that restricts the normal dynamics of EF-Tu and enables the evasion of the control exerted by nucleotides on G proteins. These results highlight stabilization of a phosphorylation-induced conformational trap as an essential mechanism for phosphoregulation of bacterial translation and metabolism. We propose that this mechanism may lead to the multisite phosphorylation state observed during dormancy and stationary phase.

The use of glass beads cultivation system to study the global effect of the ppk gene inactivation in Streptomyces lividans

The glass beads cultivation system developed in our laboratory for physiological studies of filamentous microorganisms supports differentiation and allows complete recovery of bacterial colonies and their natural products from cultivation plates. Here, we used this system to study the global effect of ppk gene disruption in Streptomyces lividans. The ppk encoding the enzyme polyphosphate kinase (P) catalyses the reversible polymerisation of gamma phosphate of ATP to polyphosphates. The resulting are phosphate and energy stock polymers. Because P activity impacts the overall energetic state of the cell, it is also connected to secondary metabolite (e.g. antibiotic) biosynthesis. We analysed the global effects of the disruption of this gene including its influence on the production of pigmented antibiotics, on morphological differentiation, on the levels of ATP and on the whole cytoplasmic protein expression pattern of S. lividans. We observed that the S. lividans ppk mutant produced antibiotics earlier and in greater amount than the wild-type (wt) strain. On the other hand, we did not observe any obvious effect on colony morphological development. In agreement with the function of Ppk, we detected much lower levels of ATP in ppk- mutant than in the wt strain. Proteomic analysis revealed that the genes that were influenced by ppk inactivation included enzymes involved in carbon or nitrogen metabolism, phosphate transport and components of the cell translational machinery. We showed that the synthesis of translation elongation factor Tu is during sporulation much higher in ppk- mutant than in wild-type strain.

Eukaryote-like serine/threonine kinases and phosphatases in bacteria

Genomic studies have revealed the presence of Ser/Thr kinases and phosphatases in many bacterial species, although their physiological roles have largely been unclear. Here we review bacterial Ser/Thr kinases (eSTKs) that show homology in their catalytic domains to eukaryotic Ser/Thr kinases and their partner phosphatases (eSTPs) that are homologous to eukaryotic phosphatases. We first discuss insights into the enzymatic mechanism of eSTK activation derived from structural studies on both the ligand-binding and catalytic domains. We then turn our attention to the identified substrates of eSTKs and eSTPs for a number of species and to the implications of these findings for understanding their physiological roles in these organisms.

Comparative study of the life cycle dependent post-translation modifications of protein synthesis elongation factor Tu present in the membrane proteome of streptomycetes and mycobacteria

We present the results of analysis of membrane phosphoproteomes from individual morphological stages of Streptomyces coelicolor that reflect developmentally dependent heterogeneity and phosphorylation of intrinsic and externally added purified Strepomyces aureofaciens EF-Tu. Fast growing nonpathogenic Mycobacterium smegmatis was used as a non-differentiating actinomycetes comparative model. Streptomycetes membrane fraction was found to contain protein kinase(s) catalyzing phosphorylation of both its own and an externally added EF-Tu, whereas Mycobacterium membrane fraction contains protein kinase phosphorylating only its own EF-Tu.