Vitamin B1 (Thiamine) Metabolism and Regulation in Archaea

Thiamine is the water-soluble sulfur containing vitamin B1 that is used to form thiamine diphosphate (ThDP), an enzyme cofactor important in the metabolism of carbohydrates, amino acids and other organic molecules. ThDP is synthesized de novo by certain bacteria, archaea, yeast, fungi, plants, and protozoans. Other organisms, such as humans, rely upon thiamine transport and salvage for metabolism; thus, thiamine is considered an essential vitamin. The focus of this chapter is on the regulation and metabolism of thiamine in archaea. The review will discuss the role ThDP has as an enzyme cofactor and the catalytic and regulatory mechanisms that archaea use to synthesize, salvage and transport thiamine. Future perspectives will be articulated in terms of how archaea have advanced our understanding of thiamine metabolism, regulation and biotechnology applications

Phosphorylation and Methylation of Proteasomal Proteins of the Haloarcheon Haloferax volcanii

Proteasomes are composed of 20S core particles (CPs) of α- and β-type subunits that associate with regulatory particle AAA ATPases such as the proteasome-activating nucleotidase (PAN) complexes of archaea. In this study, the roles and additional sites of post-translational modification of proteasomes were investigated using the archaeon Haloferax volcanii as a model. Indicative of phosphorylation, phosphatase-sensitive isoforms of α1 and α2 were detected by 2-DE immunoblot. To map these and other potential sites of post-translational modification, proteasomes were purified and analyzed by tandem mass spectrometry (MS/MS). Using this approach, several phosphosites were mapped including α1 Thr147, α2 Thr13/Ser14 and PAN-A Ser340. Multiple methylation sites were also mapped to α1, thus, revealing a new type of proteasomal modification. Probing the biological role of α1 and PAN-A phosphorylation by site-directed mutagenesis revealed dominant negative phenotypes for cell viability and/or pigmentation for α1 variants including Thr147Ala, Thr158Ala and Ser58Ala. An H. volcanii Rio1p Ser/Thr kinase homolog was purified and shown to catalyze autophosphorylation and phosphotransfer to α1. The α1 variants in Thr and Ser residues that displayed dominant negative phenotypes were significantly reduced in their ability to accept phosphoryl groups from Rio1p, thus, providing an important link between cell physiology and proteasomal phosphorylation

The Complete Genome Sequence of Haloferax volcanii DS2, a Model Archaeon

a key model organism, not only for the study of halophilicity, but also for archaeal biology in general. DS2, the type strain of this species. The genome contains a main 2.848 Mb chromosome, three smaller chromosomes pHV1, 3, 4 (85, 438, 636 kb, respectively) and the pHV2 plasmid (6.4 kb).

A comparative genomics perspective on the genetic content of the alkaliphilic haloarchaeon Natrialba magadii ATCC 43099T

BACKGROUND: Natrialba magadii is an aerobic chemoorganotrophic member of the Euryarchaeota and is a dual extremophile requiring alkaline conditions and hypersalinity for optimal growth. The genome sequence of Nab. magadii type strain ATCC 43099 was deciphered to obtain a comprehensive insight into the genetic content of this haloarchaeon and to understand the basis of some of the cellular functions necessary for its survival. RESULTS: The genome of Nab. magadii consists of four replicons with a total sequence of 4,443,643 bp and encodes 4,212 putative proteins, some of which contain peptide repeats of various lengths. Comparative genome analyses facilitated the identification of genes encoding putative proteins involved in adaptation to hypersalinity, stress response, glycosylation, and polysaccharide biosynthesis. A proton-driven ATP synthase and a variety of putative cytochromes and other proteins supporting aerobic respiration and electron transfer were encoded by one or more of Nab. magadii replicons. The genome encodes a number of putative proteases/peptidases as well as protein secretion functions. Genes encoding putative transcriptional regulators, basal transcription factors, signal perception/transduction proteins, and chemotaxis/phototaxis proteins were abundant in the genome. Pathways for the biosynthesis of thiamine, riboflavin, heme, cobalamin, coenzyme F(420) and other essential co-factors were deduced by in depth sequence analyses. However, approximately 36% of Nab. magadii protein coding genes could not be assigned a function based on Blast analysis and have been annotated as encoding hypothetical or conserved hypothetical proteins. Furthermore, despite extensive comparative genomic analyses, genes necessary for survival in alkaline conditions could not be identified in Nab. magadii. CONCLUSIONS: Based on genomic analyses, Nab. magadii is predicted to be metabolically versatile and it could use different carbon and energy sources to sustain growth. Nab. magadii has the genetic potential to adapt to its milieu by intracellular accumulation of inorganic cations and/or neutral organic compounds. The identification of Nab. magadii genes involved in coenzyme biosynthesis is a necessary step toward further reconstruction of the metabolic pathways in halophilic archaea and other extremophiles. The knowledge gained from the genome sequence of this haloalkaliphilic archaeon is highly valuable in advancing the applications of extremophiles and their enzymes

Methionine Sulfoxide Reductases of Archaea

Methionine sulfoxide reductases are found in all domains of life and are important in reversing the oxidative damage of the free and protein forms of methionine, a sulfur containing amino acid particularly sensitive to reactive oxygen species (ROS). Archaea are microbes of a domain of life distinct from bacteria and eukaryotes. Archaea are well known for their ability to withstand harsh environmental conditions that range from habitats of high ROS, such as hypersaline lakes of intense ultraviolet (UV) radiation and desiccation, to hydrothermal vents of low concentrations of dissolved oxygen at high temperature. Recent evidence reveals the methionine sulfoxide reductases of archaea function not only in the reduction of methionine sulfoxide but also in the ubiquitin-like modification of protein targets during oxidative stress, an association that appears evolutionarily conserved in eukaryotes. Here is reviewed methionine sulfoxide reductases and their distribution and function in archaea

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