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HAMP domains connect extracellular sensory with intracellular signaling domains in over 7500 proteins, including histidine kinases, adenylyl cyclases, chemotaxis receptors, and phosphatases. The solution structure of an archaeal HAMP domain shows a homodimeric, four-helical, parallel coiled coil with unusual interhelical packing, related to the canonical packing by rotation of the helices. This suggests...
Glycosylation produces an abundant, diverse, and highly regulated repertoire of cellular glycans that are frequently attached to proteins and lipids. The past decade of research on glycan function has revealed that the enzymes responsible for glycosylation—the glycosyltransferases and glycosidases—are essential in the development and physiology of living organisms. Glycans participate in many key...
Rapid and reversible methods for perturbing the function of specific proteins are desirable tools for probing complex biological systems. We have developed a general technique to regulate the stability of specific proteins in mammalian cells using cell-permeable, synthetic molecules. We engineered mutants of the human FKBP12 protein that are rapidly and constitutively degraded when expressed in mammalian...
Both genetic approaches and small-molecule inhibitors can be used to perturb protein function. Banaszynski et al. (2006) now describe a strategy to regulate the stability of a target protein, in which specificity is provided by a genetically encoded tag and temporal control is imparted by a small molecule.
Sir2 is an NAD-dependent deacetylase that connects metabolism with longevity in yeast, flies, and worms. Mammals have seven Sir2 homologs (SIRT1–7). We show that SIRT4 is a mitochondrial enzyme that uses NAD to ADP-ribosylate and downregulate glutamate dehydrogenase (GDH) activity. GDH is known to promote the metabolism of glutamate and glutamine, generating ATP, which promotes insulin secretion....
Bacterial replicative DNA polymerases such as Polymerase III (Pol III) share no sequence similarity with other polymerases. The crystal structure, determined at 2.3 Å resolution, of a large fragment of Pol III (residues 1–917), reveals a unique chain fold with localized similarity in the catalytic domain to DNA polymerase β and related nucleotidyltransferases. The structure of Pol III is strikingly...
Recent studies have shown that the synthesis of various polysaccharides by bacteria can induce immune responses that are beneficial to the bacterium, the host, or both. Here, we discuss the diverse interactions between bacterial glycans and the host immune system.
The Hox genes encode homeodomain transcription factors that are crucial for body patterning during development. Hox genes exist in clusters and their chromosomal order mimics their spatial and temporal order of expression during embryonic development. This issue's Developmental Biology Select examines recent studies that shed further light on the key roles of Hox genes and their relatives during development...
The HAMP domain is present in a large number of transmembrane proteins in prokaryotes including histidine kinases, adenylyl cyclases, chemotaxis receptors, and phosphatases. In this issue of Cell, Hulko et al. (2006) report the NMR structure of a HAMP domain and present data suggesting that it transduces signals through a simple rotation of its four-helix parallel coiled coil.
A key step in bacterial endospore formation is engulfment, during which one bacterial cell engulfs another in a phagocytosis-like process that normally requires SpoIID, SpoIIM, and SpoIIP (DMP). We here describe a second mechanism involving the zipper-like interaction between the forespore protein SpoIIQ and its mother cell ligand SpoIIIAH, which are essential for engulfment when DMP activity is reduced...
The cis-trans isomerization of proline serves as a regulatory switch in signaling pathways. We identify the proline isomerase Fpr4, a member of the FK506 binding protein family in Saccharomyces cerevisiae, as an enzyme which binds the amino-terminal tail of histones H3 and H4 and catalyses the isomerization of H3 proline P30 and P38 in vitro. We show that P38 is necessary for methylation of K36 and...
The remarkable structural diversity of glycans in nature, and their roles in cellular processes, host-pathogen interactions, biological diversity and speciation can be explained by evolutionary processes.
Successful advances in biomedical research increasingly require multigroup collaborations and publication of results in multiauthored papers. It is essential to consider at the outset how to maximize the value of such collaborations while avoiding potential pitfalls.
The crystal structure of Thermus aquaticus DNA polymerase III α subunit reveals that the structure of the catalytic domain of the eubacterial replicative polymerase is unrelated to that of the eukaryotic replicative polymerase but rather belongs to the Polβ-like nucleotidyltransferase superfamily. A model of the polymerase complexed with both DNA and β-sliding clamp interacting with a reoriented binding...
Microbial entry into host tissue is a critical first step in causing infection in animals and plants. In plants, it has been assumed that microscopic surface openings, such as stomata, serve as passive ports of bacterial entry during infection. Surprisingly, we found that stomatal closure is part of a plant innate immune response to restrict bacterial invasion. Stomatal guard cells of Arabidopsis...
Despite their initial characterization as histone deacetylases controlling transcription, sirtuins also turn out to be critical regulators of metabolism. In this issue of Cell, Haigis et al. (2006) demonstrate that the mammalian Sir2 homolog SIRT4 acts in the mitochondria of pancreatic β cells to repress the activity of glutamate dehydrogenase through ADP-ribosylation. In this way, SIRT4 downregulates...
Mutation in the TSC2 tumor suppressor causes tuberous sclerosis complex, a disease characterized by hamartoma formation in multiple tissues. TSC2 inhibits cell growth by acting as a GTPase-activating protein toward Rheb, thereby inhibiting mTOR, a central controller of cell growth. Here, we show that Wnt activates mTOR via inhibiting GSK3 without involving β-catenin-dependent transcription. GSK3 inhibits...
The TSC1/2 tumor-suppressor complex controls protein synthesis through the regulation of mTOR. In this issue of Cell, Inoki et al. (2006) report that the kinases GSK3 and AMPK cooperate in the activation of TSC2 to inhibit mTOR activity. Surprisingly, the phosphorylation of TSC2 by GSK3 is markedly suppressed by Wnt signaling. This suggests that components of the mTOR pathway may be therapeutic targets...
Ca 2+ binding to synaptotagmin 1 triggers fast exocytosis of synaptic vesicles that have been primed for release by SNARE-complex assembly. Besides synaptotagmin 1, fast Ca 2+ -triggered exocytosis requires complexins. Synaptotagmin 1 and complexins both bind to assembled SNARE complexes, but it is unclear how their functions are coupled. Here we propose that complexin binding activates...
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