Eukaryotic-like Ser/Thr Protein Kinases SpkC/F/K Are Involved in Phosphorylation of GroES in the Cyanobacterium Synechocystis

Serine/threonine protein kinases (STPKs) are the major participants in intracellular signal transduction in eukaryotes, such as yeasts, fungi, plants, and animals. Genome sequences indicate that these kinases are also present in prokaryotes, such as cyanobacteria. However, their roles in signal transduction in prokaryotes remain poorly understood. We have attempted to identify the roles of STPKs in response to heat stress in the prokaryotic cyanobacterium Synechocystis sp. PCC 6803, which has 12 genes for STPKs. Each gene was individually inactivated to generate a gene-knockout library of STPKs. We applied in vitro Ser/Thr protein phosphorylation and phosphoproteomics and identified the methionyl-tRNA synthetase, large subunit of RuBisCO, 6-phosphogluconate dehydrogenase, translation elongation factor Tu, heat-shock protein GrpE, and small chaperonin GroES as the putative targets for Ser/Thr phosphorylation. The expressed and purified GroES was used as an external substrate to screen the protein extracts of the individual mutants for their Ser/Thr kinase activities. The mutants that lack one of the three protein kinases, SpkC, SpkF, and SpkK, were unable to phosphorylate GroES in vitro, suggesting possible interactions between them towards their substrate. Complementation of the mutated SpkC, SpkF, and SpkK leads to the restoration of the ability of cells to phosphorylate the GroES. This suggests that these three STPKs are organized in a sequential order or a cascade and they work one after another to finally phosphorylate the GroES.     

At the beginning of the route: ABA perception and signal transduction in plants

Nowadays, fundamentally important data toward the molecular mechanisms of phytohormone action, starting from hormonal signal perception and up to changes in hormone-regulated gene expression, became available. Signaling mechanisms for plant cell responses to ABA remained the least known. Although a substantial progress was achieved in our understanding of the role of protein kinases and protein phosphatases functioning downstream receptors, identification of ABA receptors has induced very hot debates. This review summarizes information obtained during the last decade and concerned the molecular mechanisms of perception and signal transduction of ABA signal in plants.     

Plant cell proliferation and its regulators

Plant growth, where one of the key processes is cell division, is controlled by phytohormones. In this mini-review, an analysis of the literature on the molecular mechanisms controlling plant cell proliferation by phytohormones is presented.     

Protein quantification

Protein quantification is an integral part of any investigation related to protein isolation, purification, characterization, and analysis. Although the methods considered in this lecture have multi-year history and applied widely in the laboratory practice, there are some crucial points, which must be taken into consideration while choosing the method permitting reliably and with a high specificity and reproducibility to quantify protein.