Thiol‐based redox sensing in the methyltransferase associated sensor kinase RdmS in Methanosarcina acetivorans

Transcriptional regulation of methanogenic metabolism in archaea

Methanogenesis is a widespread metabolism of evolutionary and environmental importance that is likely to have originated on early Earth. Microorganisms that perform methanogenesis, termed methanogens, belong exclusively to the domain Archaea. Despite maintaining eukaryotic transcription machinery and homologs of bacterial regulators, archaeal transcription and gene regulation appear to be distinct from either domain. While genes involved in methanogenic metabolism have been identified and characterized, their regulation in response to both extracellular and intracellular signals is less understood. Here, we review recent reports on transcriptional regulation of methanogenesis using two model methanogens, Methanococcus maripaludis and Methanosarcina acetivorans, and highlight directions for future research in this nascent field.

Construction of a new T7 promoter compatible Escherichia coli Nissle 1917 strain for recombinant production of heme-dependent proteins

Background

Heme proteins and heme-derived molecules are essential in numerous cellular processes. Research into their in vitro functionality requires the production of large amounts of protein. Unfortunately, high yield expression is hampered by the lack of E. coli strains naturally capable of taking up heme from the medium. We recently reported the use of the probiotic E. coli strain Nissle 1917 (EcN) to sufficiently produce heme containing proteins, as it encodes the outer membrane heme receptor, ChuA, which allows for natural uptake of heme. The EcN strain however lacks the gene for T7 RNA polymerase, which is necessary for the expression of genes under the control of the T7-promotor, widely used in expression vectors like the pET or pDuet series.

Results

A new T7-promoter compatible EcN strain was constructed by integrating the gene for T7-RNA polymerase under the control of a lacUV5 promoter into the malEFG operon of EcN. Test expressions of genes via T7 promoter-based vectors in the new EcN(T7) strain were successful. Expression in EcN(T7) resulted in the efficient production of recombinant heme proteins in which the heme cofactor was incorporated during protein production. In addition, the new EcN(T7) strain can be used to co-express genes for the production of heme-derived molecules like biliverdin or other linear tetrapyrroles. We demonstrate the successful recombinant production of the phytochromes BphP, from Pseudomonas aeruginosa, and Cph1, from Synechocystis sp. PCC6803, loaded with their linear tetrapyrrole cofactors, biliverdin and phycocyanobilin, respectively.

Conclusion

We present a new E. coli strain for efficient production of heme proteins and heme-derived molecules using T7-promoter based expression vectors. The new EcN(T7) strain enables the use of a broader spectrum of expression vectors, as well as the co-expression of genes using the pDuet expression vectors, for expressing heme containing proteins. By utilizing E. coli strains EcN and EcN(T7), capable of being fed heme, the rate limiting step of heme biosynthesis in E. coli is eliminated, thereby permitting higher heme saturation of heme proteins and also higher yields of heme-derived molecules.

All living cells are cognitive

All living cells sense and respond to changes in external or internal conditions. Without that cognitive capacity, they could not obtain nutrition essential for growth, survive inevitable ecological changes, or correct accidents in the complex processes of reproduction. Wherever examined, even the smallest living cells (prokaryotes) display sophisticated regulatory networks establishing appropriate adaptations to stress conditions that maximize the probability of survival. Supposedly "simple" prokaryotic organisms also display remarkable capabilities for intercellular signalling and multicellular coordination. These observations indicate that all living cells are cognitive.

Regulation of Protein Post-Translational Modifications on Metabolism of Actinomycetes

Protein post-translational modification (PTM) is a reversible process, which can dynamically regulate the metabolic state of cells through regulation of protein structure, activity, localization or protein–protein interactions. Actinomycetes are present in the soil, air and water, and their life cycle is strongly determined by environmental conditions. The complexity of variable environments urges Actinomycetes to respond quickly to external stimuli. In recent years, advances in identification and quantification of PTMs have led researchers to deepen their understanding of the functions of PTMs in physiology and metabolism, including vegetative growth, sporulation, metabolite synthesis and infectivity. On the other hand, most donor groups for PTMs come from various metabolites, suggesting a complex association network between metabolic states, PTMs and signaling pathways. Here, we review the mechanisms and functions of PTMs identified in Actinomycetes, focusing on phosphorylation, acylation and protein degradation in an attempt to summarize the recent progress of research on PTMs and their important role in bacterial cellular processes.

Redox and Thiols in Archaea

Low molecular weight (LMW) thiols have many functions in bacteria and eukarya, ranging from redox homeostasis to acting as cofactors in numerous reactions, including detoxification of xenobiotic compounds. The LMW thiol, glutathione (GSH), is found in eukaryotes and many species of bacteria. Analogues of GSH include the structurally different LMW thiols: bacillithiol, mycothiol, ergothioneine, and coenzyme A. Many advances have been made in understanding the diverse and multiple functions of GSH and GSH analogues in bacteria but much less is known about distribution and functions of GSH and its analogues in archaea, which constitute the third domain of life, occupying many niches, including those in extreme environments. Archaea are able to use many energy sources and have many unique metabolic reactions and as a result are major contributors to geochemical cycles. As LMW thiols are major players in cells, this review explores the distribution of thiols and their biochemistry in archaea.

What do archaeal and eukaryotic histidine kinases sense?

Signal transduction systems configured around a core phosphotransfer step between a histidine kinase and a cognate response regulator protein occur in organisms from all domains of life. These systems, termed two-component systems, constitute the majority of multi-component signaling pathways in Bacteria but are less prevalent in Archaea and Eukarya. The core signaling domains are modular, allowing versatility in configuration of components into single-step phosphotransfer and multi-step phosphorelay pathways, the former being predominant in bacteria and the latter in eukaryotes. Two-component systems regulate key cellular regulatory processes that provide adaptive responses to environmental stimuli and are of interest for the development of antimicrobial therapeutics, biotechnology applications, and biosensor engineering. In bacteria, two-component systems have been found to mediate responses to an extremely broad array of extracellular and intracellular chemical and physical stimuli, whereas in archaea and eukaryotes, the use of two-component systems is more limited. This review summarizes recent advances in exploring the repertoire of sensor histidine kinases in the Archaea and Eukarya domains of life.

Spectroscopic characterization of the heme binding (GAF) domain of two sensor kinases from Methanosarcina acetivorans

The sensor kinases MsmS and RdmS from the methanogenic archaeon Methanosarcina acetivorans are multidomain proteins containing a covalently linked heme cofactor. This cofactor is connected via a single cysteine residue in a GAF domain. Although both proteins were shown to display a redox-dependent control of the downstream kinase module, this property appears to be independent of the heme cofactor. We therefore envision an additional sensor role for the heme cofactor. In order to learn more about the heme binding pocket and its constitution, UV-vis spectroscopy in combination with site-directed mutagenesis was performed on the isolated heme-binding sGAF2 domain and the full-length protein. The data indicate a 6-coordinated heme with a proximal histidine ligand and a smaller ligand, likely a water molecule on the distal site. The latter is also thought to be the sensory site and is shown to easily undergo ligand exchange.