SUMMARY Age-related frailty may be due to decreased skeletal muscle regeneration. The role of TGF-β molecules myostatin and GDF11 in regeneration is unclear. Recent studies showed an age-related decrease in GDF11 and that GDF11 treatment improves muscle regeneration, which were contrary to prior studies. We now show that these recent claims are not reproducible and the reagents previously used to detect GDF11 are not GDF11 specific. We develop a GDF11-specific immunoassay and show a trend toward increased GDF11 levels in sera of aged rats and humans. GDF11 mRNA increases in rat muscle with age. Mechanistically, GDF11 and myostatin both induce SMAD2/3 phosphorylation, inhibit myoblast differentiation, and regulate identical downstream signaling. GDF11 significantly inhibited muscle regeneration and decreased satellite cell expansion in mice. Given early data in humans showing a trend for an age-related increase, GDF11 could be a target for pharmacologic blockade to treat age-related sarcopenia.

The small ribosomal subunit is responsible for the decoding of genetic information and plays a key role in the initiation of protein synthesis. We analyzed by X-ray crystallography the structures of three different complexes of the small ribosomal subunit of Thermus thermophilus with the A-site inhibitor tetracycline, the universal initiation inhibitor edeine and the C-terminal domain of the translation initiation factor IF3. The crystal structure analysis of the complex with tetracycline revealed the functionally important site responsible for the blockage of the A-site. Five additional tetracycline sites resolve most of the controversial biochemical data on the location of tetracycline. The interaction of edeine with the small subunit indicates its role in inhibiting initiation and shows its involvement with P-site tRNA. The location of the C-terminal domain of IF3, at the solvent side of the platform, sheds light on the formation of the initiation complex, and implies that the anti-association activity of IF3 is due to its in¯uence on the conformational dynamics of the small ribosomal subunit.

Thermus thermophilus HB27 is an extremely thermophilic, halotolerant bacterium, which was originally isolated from a natural thermal environment in Japan. This organism has considerable biotechnological potential; many thermostable proteins isolated from members of the genus Thermus are indispensable in research and in industrial applications. We present here the complete genome sequence of T. thermophilus HB27, the first for the genus Thermus. The genome consists of a 1,894,877 base pair chromosome and a 232,605 base pair megaplasmid, designated pTT27. The 2,218 identified putative genes were compared to those of the closest relative sequenced so far, the mesophilic bacterium Deinococcus radiodurans. Both organisms share a similar set of proteins, although their genomes lack extensive synteny. Many new genes of potential interest for biotechnological applications were found in T. thermophilus HB27. Candidates include various proteases and key enzymes of other fundamental biological processes such as DNA replication, DNA repair and RNA maturation.

The F 420 H 2 dehydrogenase is part of the energy conserving electron transport system of the methanogenic archaeon Methanosarcina mazei Gö 1. Here it is shown that cofactor F 420 H 2 -dependent reduction of 2-hydroxyphenazine as catalyzed by the membrane-bound enzyme is coupled to proton translocation across the cytoplasmic membrane, exhibiting a stoichiometry of 0.9 H Methanosarcina mazei strain Gö1 is a strictly anaerobic methanogenic archaeon that converts a limited number of simple substrates (H 2 ϩ CO 2 , methanol, methylamines, and acetate) to methane. 2-methylthioethanesulfonate is the central intermediate in all methanogenic pathways and is reductively demethylated to methane catalyzed by the 2-methylthioethanesulfonate reductase. The two electrons required for the reduction are derived from 7-mercaptoheptanoylthreonine phosphate, resulting in the formation of a heterodisulfide (CoB-S-S-CoM) 1 of 2-mercaptoethanesulfonate (HS-CoM) and 7-mercaptoheptanoylthreonine phosphate (HS-CoB) (1). An energyconserving step in the metabolism of methanogens is the reduction of CoB-S-S-CoM with either molecular hydrogen or reduced coenzyme F 420 . In recent years, the membrane-bound electron transfer of M. mazei Gö1 has been analyzed in detail, resulting in the discovery of two proton translocating systems referred to as H 2 :heterodisulfide oxidoreductase and F 420 H 2 : heterodisulfide oxidoreductase, respectively (2).During growth on methylated substrates, part of the methyl groups of the substrates is oxidized to CO 2 , and reducing equivalents are transferred to F 420 . The reduced cofactor (F 420 H 2 ) is reoxidized by the above-mentioned membrane-bound electron transport system consisting of an F 420 H 2 dehydrogenase and a heterodisulfide reductase. The transfer of electrons between the enzymes is most likely mediated by methanophenazine, a hydrophobic cofactor that has been isolated from the cytoplasmic membrane of M. mazei Gö1. The overall process has been shown to be competent in driving proton translocation across the cytoplasmic membrane (3). The resulting electrochemical proton gradient is the driving force for ATP synthesis from ADP ϩ P i catalyzed by an A 1 A 0 -type ATP synthase (2, 4).The F 420 H 2 dehydrogenase with a molecular mass of 115 kDa has been purified from M. mazei Gö1 and contains iron-sulfur clusters and FAD (5). The isolated enzyme is very similar to the corresponding protein from Methanolobus tindarius (6) and is composed of five different subunits with molecular masses of 40, 37, 22, 20, and 17 kDa. A F 420 H 2 dehydrogenase has also been purified form the sulfate-reducing archaeon Archaeoglobus fulgidus (7).In this report the gene locus encoding the F 420 H 2 dehydrogenase on the M. mazei genome is described. Furthermore, it is shown that the corresponding enzyme is a novel proton pump ¶ To whom correspondence should be addressed. Fax: 49-551-393793; E-mail: udeppen@gwdg.de. 1 The abbreviations used are: CoB-S-S-CoM, heterodisulfide of HSCoM and HS-CoB; HS-CoM, 2-mercaptoethansulfona...

The majority of cancer patients with advanced disease experience weight loss, including loss of lean body mass. Severe weight loss is characteristic for cancer cachexia, a condition that significantly impairs functional status and survival. The underlying causes of cachexia are incompletely understood, and currently no therapeutic approach can completely reverse the condition. Autophagy coordinates lysosomal destruction of cytosolic constituents and is systemically induced by starvation. We hypothesized that starvation-mimicking signaling compounds secreted from tumor cells may cause a systemic acceleration of autophagy during cachexia. We found that IL-6 secreted by tumor cells accelerates autophagy in myotubes when complexed with soluble IL-6 receptor (trans-signaling). In lung cancer patients, were cachexia is prevalent, there was a significant correlation between elevated IL-6 expression in the tumor and poor prognosis of the patients. We found evidence for an autophagy-inducing bioactivity in serum from cancer patients and that this is clearly associated with weight loss. Importantly, the autophagy-inducing bioactivity was reduced by interference with IL-6 trans-signaling. Together, our findings suggest that IL-6 trans-signaling may be targeted in cancer cachexia.