SummaryStable isotope labelling of amino acids in cell culture (SILAC) is a quantitative proteomic method that can illuminate new pathways used by cells to adapt to different lifestyles and niches. Archaea, while thriving in extreme environments and accounting for $20%-40% of the Earth's biomass, have not been analyzed with the full potential of SILAC. Here, we report SILAC for quantitative comparison of archaeal proteomes, using Haloferax volcanii as a model. A double auxotroph was generated that allowed for complete incorporation of C-arginine such that each peptide derived from trypsin digestion was labelled. This strain was found amenable to multiplex SILAC by case study of responses to oxidative stress by hypochlorite. A total of 2565 proteins was identified by LC-MS/MS analysis (q-value 0.01) that accounted for 64% of the theoretical proteome. Of these, 176 proteins were altered at least 1.5-fold (p-value < 0.05) in abundance during hypochlorite stress. Many of the differential proteins were of unknown function. Those of known function included transcription factor homologs related to oxidative stress by 3D-homology modelling and orthologous group comparisons. Thus, SILAC is found to be an ideal method for quantitative proteomics of archaea that holds promise to unravel gene function.

DeoR-type helix-turn-helix (HTH) domain proteins are transcriptional regulators of sugar and nucleoside metabolism in diverse bacteria and occur in select archaea. In the model archaeon , previous work implicated GlpR, a DeoR-type transcriptional regulator, in transcriptional repression of and the gene encoding the fructose-specific phosphofructokinase () during growth on glycerol. However, the global regulon governed by GlpR remained unclear. Here we compared transcriptomes of wild type and Δ mutant strains grown on glycerol and glucose to detect significant transcript level differences for nearly 50 new genes regulated by GlpR. By coupling computational prediction of GlpR binding sequences with and DNA binding experiments, we determined that GlpR directly controls genes encoding enzymes in fructose degradation, including fructose bisphosphate aldolase, a central control point in glycolysis. GlpR also directly controls other transcription factors. In contrast, other metabolic pathways appear to be under indirect influence of GlpR. experiments demonstrated that GlpR purifies as a tetramer that binds the effector molecule fructose-1-phosphate (F1P). These results suggest that GlpR functions as a direct negative regulator of fructose degradation during growth on carbon sources other than fructose, such as glucose and glycerol, and that GlpR bears striking functional similarity to bacterial DeoR-type regulators.Many archaea are extremophiles, able to thrive in habitats of extreme salinity, pH and temperature. These biological properties are ideal for applications in biotechnology. However, limited knowledge of archaeal metabolism is a bottleneck that prevents broad use of archaea as microbial factories for industrial products. Here we characterize how sugar uptake and use is regulated in a species that lives in high salinity. We demonstrate that a key sugar regulatory protein in this archaeal species functions using molecular mechanisms conserved with distantly related bacterial species.

Soluble inorganic pyrophosphatases (PPAs) that hydrolyze inorganic pyrophosphate (PP i ) to orthophosphate (P i ) are commonly used to accelerate and detect biosynthetic reactions that generate PP i as a by-product. Current PPAs are inactivated by high salt concentrations and organic solvents, which limits the extent of their use. Here we report a class A type PPA of the haloarchaeon Haloferax volcanii (HvPPA) that is thermostable and displays robust PP i -hydrolyzing activity under conditions of 25% (vol/vol) organic solvent and salt concentrations from 25 mM to 3 M. HvPPA was purified to homogeneity as a homohexamer by a rapid two-step method and was found to display non-Michaelis-Menten kinetics with a V max of 465 U · mg ؊1 for PP i hydrolysis (optimal at 42°C and pH 8.5) and Hill coefficients that indicated cooperative binding to PP i and Mg 2؉ . Similarly to other class A type PPAs, HvPPA was inhibited by sodium fluoride; however, hierarchical clustering and three-dimensional (3D) homology modeling revealed HvPPA to be distinct in structure from characterized PPAs. In particular, HvPPA was highly negative in surface charge, which explained its extreme resistance to organic solvents. To demonstrate that HvPPA could drive thermodynamically unfavorable reactions to completion under conditions of reduced water activity, a novel coupled assay was developed; HvPPA hydrolyzed the PP i by-product generated in 2 M NaCl by UbaA (a "salt-loving" noncanonical E1 enzyme that adenylates ubiquitin-like proteins in the presence of ATP). Overall, we demonstrate HvPPA to be useful for hydrolyzing PP i under conditions of reduced water activity that are a hurdle to current PPA-based technologies. Inorganic pyrophosphatases (PPAs) (EC 3.6.1.1) catalyze the hydrolysis of the phosphoanhydride bond of inorganic pyrophosphate (PP i ) (P 2 O 7 4Ϫ ) to form 2 mol of orthophosphate (P i ) (PO 4 3Ϫ ) (1). PP i is a common by-product of metabolism, including the biosynthesis of DNA, RNA, protein, peptidoglycan, lipids (e.g., cholesterol), cellulose, starch, and other biopolymers (2). PP i is also formed during the posttranslational modification of proteins, including adenylation, uridylation, and ubiquitylation (2).The hydrolysis of PP i by PPA releases a considerable amount of energy (⌬G=°ϭ Ϫ19.2 kJ/mol) that can drive unfavorable biochemical transformations to completion. One example is in the synthesis of DNA by DNA polymerase. In this endergonic (⌬G=°ϭ ϩ2.1 kJ/mol) reaction, the 3=-hydroxyl group of the nucleotide that resides at the 3= end of the growing DNA strand serves as a nucleophile in the attack of the ␣ phosphorus of the incoming deoxynucleoside 5=-triphosphate (dNTP), thus releasing PP i (2). The polymerization of DNA is highly dependent on PPA to hydrolyze the energy-rich PP i to 2P i and to drive the synthesis reaction forward (2). Under standard conditions, DNA polymerase alone converts DNA to dNTPs.PPAs are used in a wide variety of biotechnology applications based on the ability of these enzymes to drive reactions f...

Halophilic archaea thrive in hypersaline conditions associated with desiccation, ultraviolet (UV) irradiation and redox active compounds, and thus are naturally tolerant to a variety of stresses. Here, we identified mutations that promote enhanced tolerance of halophilic archaea to redox-active compounds using Haloferax volcanii as a model organism. The strains were isolated from a library of random transposon mutants for growth on high doses of sodium hypochlorite (NaOCl), an agent that forms hypochlorous acid (HOCl) and other redox acid compounds common to aqueous environments of high concentrations of chloride. The transposon insertion site in each of twenty isolated clones was mapped using the following: (i) inverse nested two-step PCR (INT-PCR) and (ii) semi-random two-step PCR (ST-PCR). Genes that were found to be disrupted in hypertolerant strains were associated with lysine deacetylation, proteasomes, transporters, polyamine biosynthesis, electron transfer, and other cellular processes. Further analysis revealed a ΔpsmA1 (α1) markerless deletion strain that produces only the α2 and β proteins of 20S proteasomes was hypertolerant to hypochlorite stress compared with wild type, which produces α1, α2, and β proteins. The results of this study provide new insights into archaeal tolerance of redox active compounds such as hypochlorite.

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