Thermoproteus

The dicarboxylate/4-hydroxybutyrate cycle starts from acetyl-CoA, which is reductively carboxylated to pyruvate. Pyruvate is converted to PEP and then car-boxylated to oxaloacetate. The latter is reduced to succinyl-CoA by the reactions of an incomplete reductive citric acid cycle. Succinyl-CoA is reduced to 4-hydroxybu-tyrate, the subsequent conversion of which into two acetyl-CoA molecules proceeds in the same way as in the 3-hydroxypropionate/4-hydroxybutyrate cycle. The cycle can be divided into part 1 transforming acetyl-CoA, one C02 and one bicarbonate to succinyl-CoA via pyruvate, PEP, and oxaloacetate, and part 2 converting succinyl-CoA via 4-hydroxybutyrate into two molecules of acetyl-CoA. This cycle was shown to function in Igrticoccus hospitalis, an anaerobic autotrophic hyperther-mophilic Archaeum (Desulfurococcales) [40]. Moreover, this pathway functions in Thermoproteus neutrophilus (Thermoproteales), where the reductive citric acid cycle was earlier assumed to operate, but was later disproved (W.H. Ramos-Vera et al., unpublished results). 

AMP-dependent synthetases of eubacteria, eukaryotes, methanogens and Thermoproteus neutrophilus, where the enzyme is thought to function in the activation of acetate to acetyl-CoA (see ref. [1] and references therein). 

Fig. 17. Models of the pseudo-periplasmatic space in archaea. The pseudoperiplasmatic space is a region between the membrane and the porous outer canopy of the S-layer, which is maintained by regularly disposed spacer elements. The S-layer protein is either anchored directly in the membrane, for instance in Thermoproteus and Halobacterium, or interacts with a distinct membrane-embedded protein, as presumably in Sulfolobus. Modified from ref. [140].

Fig. 18. Thin section of Thermoproteus tenax showing an extremely wide S-layer. Courtesy of...

Fig. 19. Three-dimensional reconstruction of the (a) outer and (b,c) inner surface of the S-layer of Thermoproteus tenax. The pillars have been truncated into (a) and (b) near their bases. They are shown in their full height in (c), the view at a glancing angle of the inner surface. From ref. [132].

Considering the multitude of patterns, it is difficult to think of any common fimction for S-layers. In some cases, the S-layer contributes to the stability of the cell, similar to murein or pseudomurein cell-wall sacculi, for instance in Thermoproteus tenax which possesses an extremely stable S-layer. In many cases, the interspace between the... 

Despite the limited number of extreme thermophile species that have been examined for lipids, it appears that a few genera. Thermoplasma, Sulfolobus, Thermoproteus, Desulfurococcus, Thermococcus and Pyrococcus may be distinguished by their glycolipid and phosphoglycolipid compositions. However, it should be noted that genera in the Order Sulfolobales examined so far, such as Sulfolobus, Desulfurolobus and Metallosphaera have very similar lipid patterns, and it would be difficult to differentiate between them on the basis only of their lipids. 

Sulfolobus B12, DesuHurococcus mobilis, Thermoproteus tenax (archaea)... 

Fig. 2. The peptidyltransferase center. The structure of the central loop of Domain V of E. coli 23S rRNA is shown. Nucleotides involved in resistance against different inhibitors are indicated. Closed symbols indicate resistance and open symbols protection against chemical modification by bound antibiotic. Mutations that confer resistance to anisomycin in archaea are indicated [87] (Hcu, Halobacterium cutirubrum Hha, H. halobium). The presence of either a G or U at position 2058 in archaea is also indicated. As a consequence of this change archaea are resistant to erythromycin (Hmo, Halococcus morrhuae, Mva, Methanococcus vannielii Tte, Thermoproteus lenax Dmo, Desulfurococcus wofirfo) [29,30,88,90]. Positions where crosslinking to photoreactive derivatives of Phe-tRNA and puromycin have been observed as well as nucleotides protected by bound tRNA are also indicated. Modified from ref [73].

Thermophile High temperature Moderate thermophiles (45-65°C) Thermophiles (65-85°C) Hyperthermophiles (>85°C) Amylases, xylanases Proteases, DNA polymerases Methanobacterium, Thermoplasma, Thermus, some Bacillus species, Aquifes, Archaec lobus, Hydrogenobacter, Methanothermus, Pyrococcus, Pyrodictium, Pyrolobus, Sulfolobus, Thermococcus, Thermoproteus, Thermotoga ... 

Schramm, A. Siebers, B. Tjaden, B. Brinkmann, H. Hensel, R. Pyruvate kinase of the hyperthermophilic crenarchaeote Thermoproteus tenax physiological role and phylogenetic aspects. J. Bacteriol., 182, 2001-2009 (2000)... 

Siebers, B. Hensel, R. Pyrophosphate-dependent phosphofructokinase from Thermoproteus tenax. Methods EnzymoL, 331, 54-62 (2001)... 

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