Nickel, Iron, Sulfur Sites.

Enzymes relying on the interplay of nickel, iron, and sulfur in their active sites are used by prokaryotes to catalyze reactions driving the global carbon and hydrogen cycles. The three enzymes, [NiFe] hydrogenases, Ni,Fe-containing carbon monoxide dehydrogenases and acetyl-CoA synthases share an ancient origin possibly derived from abiotic processes. Although their active sites have different compositions and assemble Ni, Fe, and S in different ways and for different purposes, they share a central role of Ni in substrate binding and activation, with sulfur linking the Ni ion to one or more Fe ions, which, although indispensable for function, supports the catalytic process in less understood ways. The review gives a short overview on the properties of the three individual enzymes highlighting their parallels and differences.

Discovery of the Showdomycin Gene Cluster from Streptomyces showdoensis ATCC 15227 Yields Insight into the Biosynthetic Logic of C-Nucleoside Antibiotics.

Nucleoside antibiotics are a large class of pharmaceutically relevant chemical entities, which exhibit a broad spectrum of biological activities. Most nucleosides belong to the canonical N-nucleoside family, where the heterocyclic unit is connected to the carbohydrate through a carbon-nitrogen bond. However, atypical C-nucleosides were isolated from Streptomyces bacteria over 50 years ago, but the molecular basis for formation of these metabolites has been unknown. Here, we have sequenced the genome of S. showdoensis ATCC 15227 and identified the gene cluster responsible for showdomycin production. Key to the detection was the presence of sdmA, encoding an enzyme of the pseudouridine monophosphate glycosidase family, which could catalyze formation of the C-glycosidic bond. Sequence analysis revealed an unusual combination of biosynthetic genes, while inactivation and subsequent complementation of sdmA confirmed the involvement of the locus in showdomycin formation. The study provides the first steps toward generation of novel C-nucleosides by pathway engineering.

A dual function for chaperones SSB-RAC and the NAC nascent polypeptide-associated complex on ribosomes.

The yeast Hsp70/40 system SSB-RAC (stress 70 B-ribosome-associated complex) binds to ribosomes and contacts nascent polypeptides to assist cotranslational folding. In this study, we demonstrate that nascent polypeptide-associated complex (NAC), another ribosome-tethered system, is functionally connected to SSB-RAC and the cytosolic Hsp70 network. Simultaneous deletions of genes encoding NAC and SSB caused conditional loss of cell viability under protein-folding stress conditions. Furthermore, NAC mutations revealed genetic interaction with a deletion of Sse1, a nucleotide exchange factor regulating the cytosolic Hsp70 network. Cells lacking SSB or Sse1 showed protein aggregation, which is enhanced by additional loss of NAC; however, these mutants differ in their potential client repertoire. Aggregation of ribosomal proteins and biogenesis factors accompanied by a pronounced deficiency in ribosomal particles and translating ribosomes only occurs in ssbDelta and nacDeltassbDelta cells, suggesting that SSB and NAC control ribosome biogenesis. Thus, SSB-RAC and NAC assist protein folding and likewise have important functions for regulation of ribosome levels. These findings emphasize the concept that ribosome production is coordinated with the protein-folding capacity of ribosome-associated chaperones.