Immunoassay-based quantification of full-length peptidylglycine alpha-amidating monooxygenase in human plasma.

A one-step sandwich chemiluminescence immunometric assay (LIA) was developed for the quantification of bifunctional peptidylglycine-α-amidating monooxygenase (PAM) in human plasma (PAM-LIA). PAM is responsible for the activation of more than half of known peptide hormones through C-terminal α-amidation. The assay employed antibodies targeting specific catalytic PAM-subunits, peptidylglycine alpha-hydroxylating monooxygenase (PHM) and peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL), to ensure detection of full-length PAM. The PAM-LIA assay was calibrated with a human recombinant PAM enzyme and achieved a detection limit of 189 pg/mL and a quantification limit of 250 pg/mL. The assay demonstrated good inter-assay (6.7%) and intra-assay (2.2%) variabilities. It exhibited linearity when accessed by gradual dilution or random mixing of plasma samples. The accuracy of the PAM-LIA was determined to be 94.7% through spiking recovery experiments, and the signal recovery after substance interference was 94-96%. The analyte showed 96% stability after six freeze-thaw cycles. The assay showed strong correlation with matched EDTA and serum samples, as well as matched EDTA and Li-Heparin samples. Additionally, a high correlation was observed between α-amidating activity and PAM-LIA. Finally, the PAM-LIA assay was successfully applied to a sub-cohort of a Swedish population-based study, comprising 4850 individuals, confirming its suitability for routine high throughput screening.

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.

X-ray Crystallography and Vibrational Spectroscopy Reveal the Key Determinants of Biocatalytic Dihydrogen Cycling by [NiFe] Hydrogenases.

[NiFe] hydrogenases are complex model enzymes for the reversible cleavage of dihydrogen (H2 ). However, structural determinants of efficient H2 binding to their [NiFe] active site are not properly understood. Here, we present crystallographic and vibrational-spectroscopic insights into the unexplored structure of the H2 -binding [NiFe] intermediate. Using an F420 -reducing [NiFe]-hydrogenase from Methanosarcina barkeri as a model enzyme, we show that the protein backbone provides a strained chelating scaffold that tunes the [NiFe] active site for efficient H2 binding and conversion. The protein matrix also directs H2 diffusion to the [NiFe] site via two gas channels and allows the distribution of electrons between functional protomers through a subunit-bridging FeS cluster. Our findings emphasize the relevance of an atypical Ni coordination, thereby providing a blueprint for the design of bio-inspired H2 -conversion catalysts.

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.

Characterization of the DNA-binding motif of the arsenic-responsive transcription factor Yap8p.

Saccharomyces cerevisiae uses several mechanisms for arsenic detoxification including the arsenate reductase Acr2p and the arsenite efflux protein Acr3p. ACR2 and ACR3 are transcribed in opposite directions from the same promoter and expression of these genes is regulated by the AP-1 (activator protein 1)-like transcription factor Yap8p. Yap8p has been shown to permanently associate with this promoter and to stimulate ACR2/ACR3 expression in response to arsenic. In the present study we characterized the DNA sequence that is targeted by Yap8p. We show that Yap8p binds to a pseudo-palindromic TGATTAATAATCA sequence that is related to, but distinct from, the sequence recognized by other fungal AP-1 proteins. Probing the promoter by mutational analysis, we confirm the importance of the TTAATAA core element and pin-point nucleotides that flank this element as crucial for Yap8p binding and in vivo activation of ACR3 expression. A genome-wide search for this element combined with global gene expression analysis indicates that the principal function of Yap8p is to control expression of ACR2 and ACR3. We conclude that Yap8p and other yeast AP-1 proteins require distinct DNA-binding motifs to induce gene expression and propose that this fact contributed towards a separation of function between AP-1 proteins during evolution.

Mitogen-activated protein kinase Hog1 mediates adaptation to G1 checkpoint arrest during arsenite and hyperosmotic stress.

Cells slow down cell cycle progression in order to adapt to unfavorable stress conditions. Yeast (Saccharomyces cerevisiae) responds to osmotic stress by triggering G(1) and G(2) checkpoint delays that are dependent on the mitogen-activated protein kinase (MAPK) Hog1. The high-osmolarity glycerol (HOG) pathway is also activated by arsenite, and the hog1Delta mutant is highly sensitive to arsenite, partly due to increased arsenite influx into hog1Delta cells. Yeast cell cycle regulation in response to arsenite and the role of Hog1 in this process have not yet been analyzed. Here, we found that long-term exposure to arsenite led to transient G(1) and G(2) delays in wild-type cells, whereas cells that lack the HOG1 gene or are defective in Hog1 kinase activity displayed persistent G(1) cell cycle arrest. Elevated levels of intracellular arsenite and "cross talk" between the HOG and pheromone response pathways, observed in arsenite-treated hog1Delta cells, prolonged the G(1) delay but did not cause a persistent G(1) arrest. In contrast, deletion of the SIC1 gene encoding a cyclin-dependent kinase inhibitor fully suppressed the observed block of G(1) exit in hog1Delta cells. Moreover, the Sic1 protein was stabilized in arsenite-treated hog1Delta cells. Interestingly, Sic1-dependent persistent G(1) arrest was also observed in hog1Delta cells during hyperosmotic stress. Taken together, our data point to an important role of the Hog1 kinase in adaptation to stress-induced G(1) cell cycle arrest.