Isolation of a complete A1AO ATP synthase comprising nine subunits from the hyperthermophile Methanococcus jannaschii

Comparative Genomics Provides Insights into the Genetic Diversity and Evolution of the DPANN Superphylum

DPANN is known as highly diverse, globally widespread, and mostly ectosymbiotic archaeal superphylum. However, this group of archaea was overlooked for a long time, and there were limited in-depth studies reported. In this investigation, 41 metagenome-assembled genomes (MAGs) belonging to the DPANN superphylum were recovered (18 MAGs had average nucleotide identity [ANI] values of <95% and a percentage of conserved proteins [POCP] of >50%, while 14 MAGs showed a POCP of <50%), which were analyzed comparatively with 515 other published DPANN genomes. Mismatches to known 16S rRNA gene primers were identified among 16S rRNA genes of DPANN archaea. Numbers of gene families lost (mostly related to energy and amino acid metabolism) were over three times greater than those gained in the evolution of DPANN archaea. Lateral gene transfer (LGT; ∼45.5% was cross-domain) had facilitated niche adaption of the DPANN archaea, ensuring a delicate equilibrium of streamlined genomes with efficient niche-adaptive strategies. For instance, LGT-derived cytochrome bd ubiquinol oxidase and arginine deiminase in the genomes of “Candidatus Micrarchaeota” could help them better adapt to aerobic acidic mine drainage habitats. In addition, most DPANN archaea acquired enzymes for biosynthesis of extracellular polymeric substances (EPS) and transketolase/transaldolase for the pentose phosphate pathway from Bacteria.

IMPORTANCE The domain Archaea is a key research model for gaining insights into the origin and evolution of life, as well as the relevant biogeochemical processes. The discovery of nanosized DPANN archaea has overthrown many aspects of microbiology. However, the DPANN superphylum still contains a vast genetic novelty and diversity that need to be explored. Comprehensively comparative genomic analysis on the DPANN superphylum was performed in this study, with an attempt to illuminate its metabolic potential, ecological distribution and evolutionary history. Many interphylum differences within the DPANN superphylum were found. For example, Altiarchaeota had the biggest genome among DPANN phyla, possessing many pathways missing in other phyla, such as formaldehyde assimilation and the Wood-Ljungdahl pathway. In addition, LGT acted as an important force to provide DPANN archaeal genetic flexibility that permitted the occupation of diverse niches. This study has advanced our understanding of the diversity and genome evolution of archaea.

Structure and conformational plasticity of the intact Thermus thermophilus V/A-type ATPase

V (vacuolar)/A (archaeal)-type adenosine triphosphatases (ATPases), found in archaea and eubacteria, couple ATP hydrolysis or synthesis to proton translocation across the plasma membrane using the rotary-catalysis mechanism. They belong to the V-type ATPase family, which differs from the mitochondrial/chloroplast F-type ATP synthases in overall architecture. We solved cryo-electron microscopy structures of the intact Thermus thermophilus V/A-ATPase, reconstituted into lipid nanodiscs, in three rotational states and two substates. These structures indicate substantial flexibility between V₁ and V_o in a working enzyme, which results from mechanical competition between central shaft rotation and resistance from the peripheral stalks. We also describe details of adenosine diphosphate inhibition release, V₁-V_o torque transmission, and proton translocation, which are relevant for the entire V-type ATPase family.

A Na+ A1 AO ATP synthase with a V-type c subunit in a mesophilic bacterium

A₁ A_O ATP synthases with a V-type c subunit have only been found in hyperthermophilic archaea which makes bioenergetic analyses impossible due to the instability of liposomes at high temperatures. A search for a potential archaeal A₁ A_O ATP synthase with a V-type c subunit in a mesophilic organism revealed an A₁ A_O ATP synthase cluster in the anaerobic, acetogenic bacterium Eubacterium limosum KIST612. The enzyme was purified to apparent homogeneity from cells grown on methanol to a specific activity of 1.2 U·mg^-1 with a yield of 12%. The enzyme contained subunits A, B, C, D, E, F, H, a, and c. Subunit c is predicted to be a typical V-type c subunit with only one ion (Na⁺ )-binding site. Indeed, ATP hydrolysis was strictly Na⁺ -dependent. N,N'-dicyclohexylcarbodiimide (DCCD) inhibited ATP hydrolysis, but inhibition was relieved by addition of Na⁺ . Na⁺ was shown directly to abolish binding of the fluorescence DCCD derivative, NCD-4, to subunit c, demonstrating a competition of Na⁺ and DCCD/NCD-4 for a common binding site. After incorporation of the A₁ A_O ATP synthase into liposomes, ATP-dependent primary transport of ²² Na⁺ as well as ΔµNa⁺ -driven ATP synthesis could be demonstrated. The Na⁺ A₁ A_O ATP synthase from E. limosum is the first ATP synthase with a V-type c subunit from a mesophilic organism. This will enable future bioenergetic analysis of these unique ATP synthases.

Purification of a Crenarchaeal ATP Synthase in the Light of the Unique Bioenergetics of Ignicoccus Species

In this study, the ATP synthase of Ignicoccus hospitalis was purified, characterized, and structurally compared to the respective enzymes of the other Ignicoccus species, to shed light on energy conservation in this unique group of archaea. The crenarchaeal genus Ignicoccus comprises three described species, i.e., I. hospitalis and Ignicoccus islandicus from hot marine sediments near Iceland and Ignicoccus pacificus from a hydrothermal vent system in the Pacific Ocean. This genus is unique among all archaea due to the unusual cell envelope, consisting of two membranes that enclose a large intermembrane compartment (IMC). I. hospitalis is the best studied member of this genus, mainly because it is the only known host for the potentially parasitic archaeon Nanoarchaeum equitans I. hospitalis grows chemolithoautotrophically, and its sole energy-yielding reaction is the reduction of elemental sulfur with molecular hydrogen, forming large amounts of hydrogen sulfide. This reaction generates an electrochemical gradient, which is used by the ATP synthase, located in the outer cellular membrane, to generate ATP inside the IMC. The genome of I. hospitalis encodes nine subunits of an A-type ATP synthase, which we could identify in the purified complex. Although the maximal in vitro activity of the I. hospitalis enzyme was measured around pH 6, the optimal stability of the A₁A_O complex seemed to be at pH 9. Interestingly, the soluble A₁ subcomplexes of the different Ignicoccus species exhibited significant differences in their apparent molecular masses in native electrophoresis, although their behaviors in gel filtration and chromatography-mass spectrometry were very similar.IMPORTANCE The Crenarchaeota represent one of the major phyla within the Archaea domain. This study describes the successful purification of a crenarchaeal ATP synthase. To date, all information about A-type ATP synthases is from euryarchaeal enzymes. The fact that it has not been possible to purify this enzyme complex from a member of the Crenarchaeota until now points to significant differences in stability, possibly caused by structural alterations. Furthermore, the study subject I. hospitalis has a particular importance among crenarchaeotes, since it is the only known host of N. equitans The energy metabolism in this system is still poorly understood, and our results can help elucidate the unique relationship between these two microbes.

Cryo-EM studies of the structure and dynamics of vacuolar-type ATPases

Electron cryomicroscopy (cryo-EM) has significantly advanced our understanding of molecular structure in biology. Recent innovations in both hardware and software have made cryo-EM a viable alternative for targets that are not amenable to x-ray crystallography or nuclear magnetic resonance (NMR) spectroscopy. Cryo-EM has even become the method of choice in some situations where x-ray crystallography and NMR spectroscopy are possible but where cryo-EM can determine structures at higher resolution or with less time or effort. Rotary adenosine triphosphatases (ATPases) are crucial to the maintenance of cellular homeostasis. These enzymes couple the synthesis or hydrolysis of adenosine triphosphate to the use or production of a transmembrane electrochemical ion gradient, respectively. However, the membrane-embedded nature and conformational heterogeneity of intact rotary ATPases have prevented their high-resolution structural analysis to date. Recent application of cryo-EM methods to the different types of rotary ATPase has led to sudden advances in understanding the structure and function of these enzymes, revealing significant conformational heterogeneity and characteristic transmembrane α helices that are highly tilted with respect to the membrane. In this Review, we will discuss what has been learned recently about rotary ATPase structure and function, with a particular focus on the vacuolar-type ATPases.

Structural Basis for a Unique ATP Synthase Core Complex from Nanoarcheaum equitans

ATP synthesis is a critical and universal life process carried out by ATP synthases. Whereas eukaryotic and prokaryotic ATP synthases are well characterized, archaeal ATP synthases are relatively poorly understood. The hyperthermophilic archaeal parasite, Nanoarcheaum equitans, lacks several subunits of the ATP synthase and is suspected to be energetically dependent on its host, Ignicoccus hospitalis. This suggests that this ATP synthase might be a rudimentary machine. Here, we report the crystal structures and biophysical studies of the regulatory subunit, NeqB, the apo-NeqAB, and NeqAB in complex with nucleotides, ADP, and adenylyl-imidodiphosphate (non-hydrolysable analog of ATP). NeqB is ∼20 amino acids shorter at its C terminus than its homologs, but this does not impede its binding with NeqA to form the complex. The heterodimeric NeqAB complex assumes a closed, rigid conformation irrespective of nucleotide binding; this differs from its homologs, which require conformational changes for catalytic activity. Thus, although N. equitans possesses an ATP synthase core A3B3 hexameric complex, it might not function as a bona fide ATP synthase.

The a subunit of the A1AO ATP synthase of Methanosarcina mazei Gö1 contains two conserved arginine residues that are crucial for ATP synthesis

Like the evolutionary related F1FO ATP synthases and V1VO ATPases, the A1AO ATP synthases from archaea are multisubunit, membrane-bound transport machines that couple ion flow to the synthesis of ATP. Although the subunit composition is known for at least two species, nothing is known so far with respect to the function of individual subunits or amino acid residues. To pave the road for a functional analysis of A1AO ATP synthases, we have cloned the entire operon from Methanosarcina mazei into an expression vector and produced the enzyme in Escherichia coli. Inverted membrane vesicles of the recombinants catalyzed ATP synthesis driven by NADH oxidation as well as artificial driving forces. [Formula: see text] as well as ΔpH were used as driving forces which is consistent with the inhibition of NADH-driven ATP synthesis by protonophores. Exchange of the conserved glutamate in subunit c led to a complete loss of ATP synthesis, proving that this residue is essential for H+ translocation. Exchange of two conserved arginine residues in subunit a has different effects on ATP synthesis. The role of these residues in ion translocation is discussed.

Na+ transport by the A1AO-ATP synthase purified from Thermococcus onnurineus and reconstituted into liposomes

The ATP synthase of many archaea has the conserved sodium ion binding motif in its rotor subunit, implying that these A1AO-ATP synthases use Na(+) as coupling ion. However, this has never been experimentally verified with a purified system. To experimentally address the nature of the coupling ion, we have purified the A1AO-ATP synthase from T. onnurineus. It contains nine subunits that are functionally coupled. The enzyme hydrolyzed ATP, CTP, GTP, UTP, and ITP with nearly identical activities of around 40 units/mg of protein and was active over a wide pH range with maximal activity at pH 7. Noteworthy was the temperature profile. ATP hydrolysis was maximal at 80 °C and still retained an activity of 2.5 units/mg of protein at 45 °C. The high activity of the enzyme at 45 °C opened, for the first time, a way to directly measure ion transport in an A1AO-ATP synthase. Therefore, the enzyme was reconstituted into liposomes generated from Escherichia coli lipids. These proteoliposomes were still active at 45 °C and coupled ATP hydrolysis to primary and electrogenic Na(+) transport. This is the first proof of Na(+) transport by an A1AO-ATP synthase and these findings are discussed in light of the distribution of the sodium ion binding motif in archaea and the role of Na(+) in the bioenergetics of archaea.

Carbohydrate metabolism in Archaea: current insights into unusual enzymes and pathways and their regulation

The metabolism of Archaea, the third domain of life, resembles in its complexity those of Bacteria and lower Eukarya. However, this metabolic complexity in Archaea is accompanied by the absence of many "classical" pathways, particularly in central carbohydrate metabolism. Instead, Archaea are characterized by the presence of unique, modified variants of classical pathways such as the Embden-Meyerhof-Parnas (EMP) pathway and the Entner-Doudoroff (ED) pathway. The pentose phosphate pathway is only partly present (if at all), and pentose degradation also significantly differs from that known for bacterial model organisms. These modifications are accompanied by the invention of "new," unusual enzymes which cause fundamental consequences for the underlying regulatory principles, and classical allosteric regulation sites well established in Bacteria and Eukarya are lost. The aim of this review is to present the current understanding of central carbohydrate metabolic pathways and their regulation in Archaea. In order to give an overview of their complexity, pathway modifications are discussed with respect to unusual archaeal biocatalysts, their structural and mechanistic characteristics, and their regulatory properties in comparison to their classic counterparts from Bacteria and Eukarya. Furthermore, an overview focusing on hexose metabolic, i.e., glycolytic as well as gluconeogenic, pathways identified in archaeal model organisms is given. Their energy gain is discussed, and new insights into different levels of regulation that have been observed so far, including the transcript and protein levels (e.g., gene regulation, known transcription regulators, and posttranslational modification via reversible protein phosphorylation), are presented.

ATP synthases from archaea: the beauty of a molecular motor

Archaea live under different environmental conditions, such as high salinity, extreme pHs and cold or hot temperatures. How energy is conserved under such harsh environmental conditions is a major question in cellular bioenergetics of archaea. The key enzymes in energy conservation are the archaeal A1AO ATP synthases, a class of ATP synthases distinct from the F1FO ATP synthase ATP synthase found in bacteria, mitochondria and chloroplasts and the V1VO ATPases of eukaryotes. A1AO ATP synthases have distinct structural features such as a collar-like structure, an extended central stalk, and two peripheral stalks possibly stabilizing the A1AO ATP synthase during rotation in ATP synthesis/hydrolysis at high temperatures as well as to provide the storage of transient elastic energy during ion-pumping and ATP synthesis/-hydrolysis. High resolution structures of individual subunits and subcomplexes have been obtained in recent years that shed new light on the function and mechanism of this unique class of ATP synthases. An outstanding feature of archaeal A1AO ATP synthases is their diversity in size of rotor subunits and the coupling ion used for ATP synthesis with H(+), Na(+) or even H(+) and Na(+) using enzymes. The evolution of the H(+) binding site to a Na(+) binding site and its implications for the energy metabolism and physiology of the cell are discussed.

A1Ao-ATP synthase of Methanobrevibacter ruminantium couples sodium ions for ATP synthesis under physiological conditions

An unresolved question in the bioenergetics of methanogenic archaea is how the generation of proton-motive and sodium-motive forces during methane production is used to synthesize ATP by the membrane-bound A(1)A(o)-ATP synthase, with both proton- and sodium-coupled enzymes being reported in methanogens. To address this question, we investigated the biochemical characteristics of the A(1)A(o)-ATP synthase (MbbrA(1)A(o)) of Methanobrevibacter ruminantium M1, a predominant methanogen in the rumen. Growth of M. ruminantium M1 was inhibited by protonophores and sodium ionophores, demonstrating that both ion gradients were essential for growth. To study the role of these ions in ATP synthesis, the ahaHIKECFABD operon encoding the MbbrA(1)A(o) was expressed in Escherichia coli strain DK8 (Δatp) and purified yielding a 9-subunit protein with an SDS-stable c oligomer. Analysis of the c subunit amino acid sequence revealed that it consisted of four transmembrane helices, and each hairpin displayed a complete Na(+)-binding signature made up of identical amino acid residues. The purified MbbrA(1)A(o) was stimulated by sodium ions, and Na(+) provided pH-dependent protection against inhibition by dicyclohexylcarbodiimide but not tributyltin chloride. ATP synthesis in inverted membrane vesicles lacking sodium ions was driven by a membrane potential that was sensitive to cyanide m-chlorophenylhydrazone but not to monensin. ATP synthesis could not be driven by a chemical gradient of sodium ions unless a membrane potential was imposed. ATP synthesis under these conditions was sensitive to monensin but not cyanide m-chlorophenylhydrazone. These data suggest that the M. ruminantium M1 A(1)A(o)-ATP synthase exhibits all the properties of a sodium-coupled enzyme, but it is also able to use protons to drive ATP synthesis under conditions that favor proton coupling, such as low pH and low levels of sodium ions.

Structural divergence of the rotary ATPases

The rotary ATPase family of membrane protein complexes may have only three members, but each one plays a fundamental role in biological energy conversion. The F1Fo-ATPase (F-ATPase) couples ATP synthesis to the electrochemical membrane potential in bacteria, mitochondria and chloroplasts, while the vacuolar H+-ATPase (V-ATPase) operates as an ATP-driven proton pump in eukaryotic membranes. In different species of archaea and bacteria, the A1Ao-ATPase (A-ATPase) can function as either an ATP synthase or an ion pump. All three of these multi-subunit complexes are rotary molecular motors, sharing a fundamentally similar mechanism in which rotational movement drives the energy conversion process. By analogy to macroscopic systems, individual subunits can be assigned to rotor, axle or stator functions. Recently, three-dimensional reconstructions from electron microscopy and single particle image processing have led to a significant step forward in understanding of the overall architecture of all three forms of these complexes and have allowed the organisation of subunits within the rotor and stator parts of the motors to be more clearly mapped out. This review describes the emerging consensus regarding the organisation of the rotor and stator components of V-, A- and F-ATPases, examining core similarities that point to a common evolutionary origin, and highlighting key differences. In particular, it discusses how newly revealed variation in the complexity of the inter-domain connections may impact on the mechanics and regulation of these molecular machines.

The transition-like state and Pi entrance into the catalytic a subunit of the biological engine A-ATP synthase

Archaeal A-ATP synthases catalyze the formation of the energy currency ATP. The chemical mechanisms of ATP synthesis in A-ATP synthases are unknown. We have determined the crystal structure of a transition-like state of the vanadate-bound form of catalytic subunit A (A(Vi)) of the A-ATP synthase from Pyrococcus horikoshii OT3. Two orthovanadate molecules were observed in the A(Vi) structure, one of which interacts with the phosphate binding loop through residue S238. The second vanadate is positioned in the transient binding site, implicating for the first time the pathway for phosphate entry to the catalytic site. Moreover, since residues K240 and T241 are proposed to be essential for catalysis, the mutant structures of K240A and T241A were also determined. The results demonstrate the importance of these two residues for transition-state stabilization. The structures presented shed light on the diversity of catalytic mechanisms used by the biological motors A- and F-ATP synthases and eukaryotic V-ATPases.

The critical roles of residues P235 and F236 of subunit A of the motor protein A-ATP synthase in P-loop formation and nucleotide binding

The mutants P235A and F236A have been generated and their crystal structure was determined to resolutions of 2.38 and 2.35 A, respectively, in order to understand the residues involved in the formation of the novel arched P-loop of subunit A of the A-ATP synthase from Pyrococcus horikoshii OT3. Both the structures show unique, altered conformations for the P-loop. Comparison with the previously solved wild type and P-loop mutant S238A structures of subunit A showed that the P-loop conformation for these two novel mutants occupy intermediate positions, with the wild type fully arched and the well-relaxed S238A mutant structures taking the extreme positions. Even though the deviation is similar for both mutants, the curvature of the P-loop faces the opposite direction. Deviations in the GER-loop, lying above the P-loop, are similar for both mutants, but in F236A, it moves towards the P-loop by around 2 A. The curvature of the loop region V392-V410, located directly behind the P-loop, moves close by 3.6 A towards the P-loop in the F236A structure and away by 2.5 A in the P235A structure. Two major deviations were observed in the P235A mutant, which are not identified in any of the subunit A structures analyzed so far, one being a wide movement of the N-terminal loop region (R90-P110) making a rotation of 80 degrees and the other being rigid-body rotation of the C-terminal helices from Q520-A588 by around 4 degrees upwards. Taken together, the data presented demonstrate the concerted effects of the critical residues P235A, F236, and S238 in the unique P-loop conformation of the A-ATP synthases.

Energized outer membrane and spatial separation of metabolic processes in the hyperthermophilic Archaeon Ignicoccus hospitalis

ATP synthase catalyzes ATP synthesis at the expense of an electrochemical ion gradient across a membrane that can be generated by different exergonic reactions. Sulfur reduction is the main energy-yielding reaction in the hyperthermophilic strictly anaerobic Crenarchaeon Ignicoccus hospitalis. This organism is unusual in having an inner and an outer membrane that are separated by a huge intermembrane compartment. Here we show, on the basis of immuno-EM analyses of ultrathin sections and immunofluorescence experiments with whole I. hospitalis cells, that the ATP synthase and H(2):sulfur oxidoreductase complexes of this organism are located in the outer membrane. These two enzyme complexes are mandatory for the generation of an electrochemical gradient and for ATP synthesis. Thus, among all prokaryotes possessing two membranes in their cell envelope (including Planctomycetes, gram-negative bacteria), I. hospitalis is a unique organism, with an energized outer membrane and ATP synthesis within the periplasmic space. In addition, DAPI staining and EM analyses showed that DNA and ribosomes are localized in the cytoplasm, leading to the conclusion that in I. hospitalis energy conservation is separated from information processing and protein biosynthesis. This raises questions regarding the function of the two membranes, the interaction between these compartments, and the general definition of a cytoplasmic membrane.

Nucleotide binding states of subunit A of the A-ATP synthase and the implication of P-loop switch in evolution

The crystal structures of the nucleotide-empty (A(E)), 5'-adenylyl-beta,gamma-imidodiphosphate (A(PNP))-bound, and ADP (A(DP))-bound forms of the catalytic A subunit of the energy producer A(1)A(O) ATP synthase from Pyrococcus horikoshii OT3 have been solved at 2.47 A and 2.4 A resolutions. The structures provide novel features of nucleotide binding and depict the residues involved in the catalysis of the A subunit. In the A(E) form, the phosphate analog SO(4)(2-) binds, via a water molecule, to the phosphate binding loop (P-loop) residue Ser238, which is also involved in the phosphate binding of ADP and 5'-adenylyl-beta,gamma-imidodiphosphate. Together with amino acids Gly234 and Phe236, the serine residue stabilizes the arched P-loop conformation of subunit A, as shown by the 2.4-A structure of the mutant protein S238A in which the P-loop flips into a relaxed state, comparable to the one in catalytic beta subunits of F(1)F(O) ATP synthases. Superposition of the existing P-loop structures of ATPases emphasizes the unique P-loop in subunit A, which is also discussed in the light of an evolutionary P-loop switch in related A(1)A(O) ATP synthases, F(1)F(O) ATP synthases, and vacuolar ATPases and implicates diverse catalytic mechanisms inside these biological motors.

The interaction of Nanoarchaeum equitans with Ignicoccus hospitalis: proteins in the contact site between two cells

The two archaea Ignicoccus hospitalis and Nanoarchaeum equitans form a unique intimate association, the character of which is not yet fully understood. Electron microscopic investigations show that at least two modes of cell-cell interactions exist: (i) the two cells are interconnected via thin fibres; and (ii) the two cell surfaces are in direct contact with each other. In order to shed further light on the molecules involved, we isolated a protein complex, by using detergent-induced solubilization of cell envelopes, followed by a combination of chromatography steps. Analysis by MS and comparison with databases revealed that this fraction contained two dominant proteins, representing the respective major envelope proteins of the two archaea. In addition, a considerable set of membrane proteins is specifically associated with these proteins. They are now the focus of further biochemical and ultrastructural investigations.

The coupling ion in the methanoarchaeal ATP synthases: H(+) vs. Na(+) in the A(1)A(o) ATP synthase from the archaeon Methanosarcina mazei Gö1

To establish a system to analyze ATP synthesis by the archaeal A(1)A(o) ATP synthase and to address the nature of the coupling ion, the operon encoding the A(1)A(o) ATP synthase from the mesophile Methanosarcina mazei Gö1 was cloned in an expression vector and it was expressed in the F(1)F(o) ATP synthase-negative mutant Escherichia coli DK8. Western blot analyses revealed that each of the subunits was produced, and the subunits assembled to a functional, membrane-embedded ATP synthase/ATPase. ATP hydrolysis was inhibited by dicyclohexylcarbodiimide but also by tributyltin, which turned out to be the most efficient inhibitor of the A(o) domain of A(1)A(o) ATP synthase known to date. ATP hydrolysis was not dependent on the Na(+) concentration of the medium, and inhibition of the enzyme by dicyclohexylcarbodiimide could not be relieved by Na(+). The enzyme present in the cytoplasmic membrane of E. coli catalyzed ATP synthesis driven by an artificial DeltapH but not by DeltapNa or DeltamuNa(+).

A sodium ion-dependent A1AO ATP synthase from the hyperthermophilic archaeon Pyrococcus furiosus

The rotor subunit c of the A(1)A(O) ATP synthase of the hyperthermophilic archaeon Pyrococcus furiosus contains a conserved Na(+)-binding motif, indicating that Na(+) is a coupling ion. To experimentally address the nature of the coupling ion, we isolated the enzyme by detergent solubilization from native membranes followed by chromatographic separation techniques. The entire membrane-embedded motor domain was present in the preparation. The rotor subunit c was found to form an SDS-resistant oligomer. Under the conditions tested, the enzyme had maximal activity at 100 degrees C, had a rather broad pH optimum between pH 5.5 and 8.0, and was inhibited by diethystilbestrol and derivatives thereof. ATP hydrolysis was strictly dependent on Na(+), with a K(m) of 0.6 mM. Li(+), but not K(+), could substitute for Na(+). The Na(+) dependence was less pronounced at higher proton concentrations, indicating competition between Na(+) and H(+) for a common binding site. Moreover, inhibition of the ATPase by N',N'-dicyclohexylcarbodiimide could be relieved by Na(+). Taken together, these data demonstrate the use of Na(+) as coupling ion for the A(1)A(O) ATP synthase of Pyrococcus furiosus, the first Na(+) A(1)A(O) ATP synthase described.

Life close to the thermodynamic limit: how methanogenic archaea conserve energy

Methane-forming archaea are strictly anaerobic, ancient microbes that are widespread in nature. These organisms are commonly found in anaerobic environments such as rumen, anaerobic sediments of rivers and lakes, hyperthermal deep sea vents and even hypersaline environments. From an evolutionary standpoint they are close to the origin of life. Common to all methanogens is the biological production of methane by a unique pathway currently only found in archaea. Methanogens can grow on only a limited number of substrates such as H(2) + CO(2), formate, methanol and other methyl group-containing substrates and some on acetate. The free energy change associated with methanogenesis from these compounds allows for the synthesis of 1 (acetate) to a maximum of only 2 mol of ATP under standard conditions while under environmental conditions less than one ATP can be synthesized. Therefore, methanogens live close to the thermodynamic limit. To cope with this problem, they have evolved elaborate mechanisms of energy conservation using both protons and sodium ions as the coupling ion in one pathway. These energy conserving mechanisms are comprised of unique enzymes, cofactors and electron carriers present only in methanogens. This review will summarize the current knowledge of energy conservation of methanogens and focus on recent insights into structure and function of ion translocating enzymes found in these organisms.

The dominating outer membrane protein of the hyperthermophilic Archaeum Ignicoccus hospitalis: a novel pore-forming complex

The membrane protein Imp1227 (Ignicoccus outer membrane protein; Imp1227) is the main protein constituent of the unique outer sheath of the hyperthermophilic, chemolithoautotrophic Archaeum Ignicoccus hospitalis. This outer sheath is the so far only known example for an asymmetric bilayer among the Archaea and is named 'outer membrane'. With its molecular mass of only 6.23 kDa, Imp1227 is found to be incorporated into the outer membrane in form of large, stable complexes. When separated by SDS-PAGE, they exhibit apparent masses of about 150, 50, 45 and 35 kDa. Dissociation into the monomeric form is achieved by treatment with SDS-containing solutions at temperatures at or above 113 degrees C. Electron micrographs of negatively stained samples confirm that isolated membranes are tightly packed with round complexes, about 7 nm in diameter, with a central, stain-filled 2 nm pore; a local two-dimensional crystalline arrangement in form of small patches can be detected by tomographic reconstruction. The comparison of the nucleotide and amino acid sequence of Imp1227 with public databases showed no reliable similarities with known proteins. Using secondary structure prediction and molecular modelling, an alpha-helical transmembrane domain is proposed; for the oligomer, a ring-shaped nonamer with a central 2 nm pore is a likely arrangement.

Characterization of DNA transport in the thermophilic bacterium Thermus thermophilus HB27

Horizontal gene transfer has been a major force for genome plasticity over evolutionary history, and is largely responsible for fitness-enhancing traits, including antibiotic resistance and virulence factors. In particular, for adaptation of prokaryotes to extreme environments, lateral gene transfer seems to have played a crucial role. Recently, by performing a genome-wide mutagenesis approach with Thermus thermophilus HB27, we identified the first genes in a thermophilic bacterium for the uptake of free DNA, a process called natural transformation. Here, we present the first data on the biochemistry and bioenergetics of the DNA transport process in this thermophile. We report that linear and circular plasmid DNA are equally well taken up with a high maximal velocity of 1.5 microg DNA.(mg protein)(-1).min(-1), demonstrating an extremely efficient binding and uptake rate of 40 kb.s(-1).cell(-1). Uncouplers and ATPase inhibitors immediately inhibited DNA uptake, providing clear evidence that DNA translocation in HB27 is an energy-dependent process. DNA uptake studies with genomic DNA of Bacteria, Archaea and Eukarya revealed that Thermus thermophilus HB27 takes up DNA from members of all three domains of life. We propose that the extraordinary broad substrate specificity of the highly efficient Thermus thermophilus HB27 DNA uptake system may contribute significantly to thermoadaptation of Thermus thermophilus HB27 and to interdomain DNA transfer in hot environments.

Structural and functional analysis of the coupling subunit F in solution and topological arrangement of the stalk domains of the methanogenic A1AO ATP synthase

The first low-resolution shape of subunit F of the A(1)A(O) ATP synthase from the archaeon Methanosarcina mazei Gö1 in solution was determined by small angle X-ray scattering. Independent to the concentration used, the protein is monomeric and has an elongated shape, divided in a main globular part with a length of about 4.5 nm, and a hook-like domain of about 3.0 nm in length. The subunit-subunit interaction of subunit F inside the A(1)A(O) ATP synthase in the presence of 1-ethyl-3-(dimethylaminopropyl)-carbodiimide EDC was studied as a function of nucleotide binding, demonstrating movements of subunits F relative to the nucleotide-binding subunit B. Furthermore, in the intact A(1)A(O) complex, crosslinking of subunits D-E, A-H and A-B-D was obtained and the peptides, involved, were analyzed by MALDI-TOF mass spectrometry. Based on these data the surface of contact of B-F could be mapped in the high-resolution structure of subunit B of the A(1)A(O) ATP synthase.

Bioenergetics of archaea: ancient energy conserving mechanisms developed in the early history of life

A key component in cellular bioenergetics is the ATP synthase. The enzyme from archaea represents a new class of ATPases, the A1AO ATP synthases. They are composed of two domains that function as a pair of rotary motors connected by a central and peripheral stalk(s). The structure of the chemically-driven motor (A1) was solved by small angle X-ray scattering in solution, and the structure of the first A1AO ATP synthases (from methanoarchaea) was obtained recently by single particle analyses. These studies revealed novel structural features such as a second peripheral stalk and a collar-like structure. Interestingly, the membrane-embedded electrically-driven motor (AO) is very different in archaea with sometimes novel, exceptional subunit composition.

Crystal structure of the archaeal A1Ao ATP synthase subunit B from Methanosarcina mazei Gö1: Implications of nucleotide-binding differences in the major A1Ao subunits A and B

The A1Ao ATP synthase from archaea represents a class of chimeric ATPases/synthases, whose function and general structural design share characteristics both with vacuolar V1Vo ATPases and with F1Fo ATP synthases. The primary sequences of the two large polypeptides A and B, from the catalytic part, are closely related to the eukaryotic V1Vo ATPases. The chimeric nature of the A1Ao ATP synthase from the archaeon Methanosarcina mazei Gö1 was investigated in terms of nucleotide interaction. Here, we demonstrate the ability of the overexpressed A and B subunits to bind ADP and ATP by photoaffinity labeling. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to map the peptide of subunit B involved in nucleotide interaction. Nucleotide affinities in both subunits were determined by fluorescence correlation spectroscopy, indicating a weaker binding of nucleotide analogues to subunit B than to A. In addition, the nucleotide-free crystal structure of subunit B is presented at 1.5 A resolution, providing the first view of the so-called non-catalytic subunit of the A1Ao ATP synthase. Superposition of the A-ATP synthase non-catalytic B subunit and the F-ATP synthase non-catalytic alpha subunit provides new insights into the similarities and differences of these nucleotide-binding ATPase subunits in particular, and into nucleotide binding in general. The arrangement of subunit B within the intact A1Ao ATP synthase is presented.

ATP Synthases With Novel Rotor Subunits: New Insights into Structure, Function and Evolution of ATPases

ATPases with unusual membrane-embedded rotor subunits were found in both F(1)F(0) and A(1)A(0) ATP synthases. The rotor subunit c of A(1)A(0) ATPases is, in most cases, similar to subunit c from F(0). Surprisingly, multiplied c subunits with four, six, or even 26 transmembrane spans have been found in some archaea and these multiplication events were sometimes accompanied by loss of the ion-translocating group. Nevertheless, these enzymes are still active as ATP synthases. A duplicated c subunit with only one ion-translocating group was found along with "normal" F(0) c subunits in the Na(+) F(1)F(0) ATP synthase of the bacterium Acetobacterium woodii. These extraordinary features and exceptional structural and functional variability in the rotor of ATP synthases may have arisen as an adaptation to different cellular needs and the extreme physicochemical conditions in the early history of life.

Proteome of Methanosarcina acetivorans Part II: comparison of protein levels in acetate- and methanol-grown cells

Methanosarcina acetivorans is an archaeon isolated from marine sediments which utilizes a diversity of substrates for growth and methanogenesis. Part I of a two-part investigation has profiled proteins of this microorganism cultured with both methanol and acetate as growth substrates, utilizing two-dimensional gel electrophoresis and MALDI-TOF-TOF mass spectrometry. In this report, Part II, the analyses were extended to identify 34 proteins found to be present in different amounts between methanol- and acetate-grown M. acetivorans. Among these proteins are enzymes which function in pathways for methanogenesis from either acetate or methanol. Several of the 34 proteins were determined to have redundant functions based on annotations of the genomic sequence. Enzymes which function in ATP synthesis and steps common to both methanogenic pathways were elevated in acetate- versus methanol-grown cells, whereas enzymes that have a more general function in protein synthesis were in greater amounts in methanol- compared to acetate-grown cells. Several group I chaperonins were present in greater amounts in methanol- versus acetate-grown cells, whereas lower amounts of several stress related proteins were found in methanol- versus acetate-grown cells. The potential physiological basis for these novel patterns of protein synthesis are discussed.

Structure and subunit arrangement of the A-type ATP synthase complex from the archaeon Methanococcus jannaschii visualized by electron microscopy

In Archaea, bacteria, and eukarya, ATP provides metabolic energy for energy-dependent processes. It is synthesized by enzymes known as A-type or F-type ATP synthase, which are the smallest rotatory engines in nature (Yoshida, M., Muneyuki, E., and Hisabori, T. (2001) Nat. Rev. Mol. Cell. Biol. 2, 669-677; Imamura, H., Nakano, M., Noji, H., Muneyuki, E., Ohkuma, S., Yoshida, M., and Yokoyama, K. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 2312-2315). Here, we report the first projected structure of an intact A(1)A(0) ATP synthase from Methanococcus jannaschii as determined by electron microscopy and single particle analysis at a resolution of 1.8 nm. The enzyme with an overall length of 25.9 nm is organized in an A(1) headpiece (9.4 x 11.5 nm) and a membrane domain, A(0) (6.4 x 10.6 nm), which are linked by a central stalk with a length of approximately 8 nm. A part of the central stalk is surrounded by a horizontal-situated rodlike structure ("collar"), which interacts with a peripheral stalk extending from the A(0) domain up to the top of the A(1) portion, and a second structure connecting the collar structure with A(1). Superposition of the three-dimensional reconstruction and the solution structure of the A(1) complex from Methanosarcina mazei Gö1 have allowed the projections to be interpreted as the A(1) headpiece, a central and the peripheral stalk, and the integral A(0) domain. Finally, the structural organization of the A(1)A(0) complex is discussed in terms of the structural relationship to the related motors, F(1)F(0) ATP synthase and V(1)V(0) ATPases.

The genome of Nanoarchaeum equitans: insights into early archaeal evolution and derived parasitism

The hyperthermophile Nanoarchaeum equitans is an obligate symbiont growing in coculture with the crenarchaeon Ignicoccus. Ribosomal protein and rRNA-based phylogenies place its branching point early in the archaeal lineage, representing the new archaeal kingdom Nanoarchaeota. The N. equitans genome (490,885 base pairs) encodes the machinery for information processing and repair, but lacks genes for lipid, cofactor, amino acid, or nucleotide biosyntheses. It is the smallest microbial genome sequenced to date, and also one of the most compact, with 95% of the DNA predicted to encode proteins or stable RNAs. Its limited biosynthetic and catabolic capacity indicates that N. equitans' symbiotic relationship to Ignicoccus is parasitic, making it the only known archaeal parasite. Unlike the small genomes of bacterial parasites that are undergoing reductive evolution, N. equitans has few pseudogenes or extensive regions of noncoding DNA. This organism represents a basal archaeal lineage and has a highly reduced genome.