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71.
In this issue of Molecular Cell, two papers on the structure of murine capping enzyme guanylyltransferase (Ghosh et?al., 2011) and yeast studies of the recognition of the RNA polymerase II CTD (Schwer and Shuman, 2011) describe the mechanism of recruitment of the capping apparatus to nascent pre-mRNAs. 相似文献
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Kamat SS Holmes-Hampton GP Bagaria A Kumaran D Tichy SE Gheyi T Zheng X Bain K Groshong C Emtage S Sauder JM Burley SK Swaminathan S Lindahl PA Raushel FM 《Protein science : a publication of the Protein Society》2011,20(12):2080-2094
Adenine deaminase (ADE) from the amidohydrolase superfamily (AHS) of enzymes catalyzes the conversion of adenine to hypoxanthine and ammonia. Enzyme isolated from Escherichia coli was largely inactive toward the deamination of adenine. Molecular weight determinations by mass spectrometry provided evidence that multiple histidine and methionine residues were oxygenated. When iron was sequestered with a metal chelator and the growth medium supplemented with Mn2+ before induction, the post-translational modifications disappeared. Enzyme expressed and purified under these conditions was substantially more active for adenine deamination. Apo-enzyme was prepared and reconstituted with two equivalents of FeSO4. Inductively coupled plasma mass spectrometry and Mössbauer spectroscopy demonstrated that this protein contained two high-spin ferrous ions per monomer of ADE. In addition to the adenine deaminase activity, [FeII/FeII]-ADE catalyzed the conversion of H2O2 to O2 and H2O. The values of kcat and kcat/Km for the catalase activity are 200 s−1 and 2.4 × 104 M−1 s−1, respectively. [FeII/FeII]-ADE underwent more than 100 turnovers with H2O2 before the enzyme was inactivated due to oxygenation of histidine residues critical for metal binding. The iron in the inactive enzyme was high-spin ferric with gave = 4.3 EPR signal and no evidence of anti-ferromagnetic spin-coupling. A model is proposed for the disproportionation of H2O2 by [FeII/FeII]-ADE that involves the cycling of the binuclear metal center between the di-ferric and di-ferrous oxidation states. Oxygenation of active site residues occurs via release of hydroxyl radicals. These findings represent the first report of redox reaction catalysis by any member of the AHS. 相似文献
74.
Seung Joong Kim Javier Fernandez-Martinez Parthasarathy Sampathkumar Anne Martel Tsutomu Matsui Hiro Tsuruta Thomas M. Weiss Yi Shi Ane Markina-Inarrairaegui Jeffery B. Bonanno J. Michael Sauder Stephen K. Burley Brian T. Chait Steven C. Almo Michael P. Rout Andrej Sali 《Molecular & cellular proteomics : MCP》2014,13(11):2911-2926
75.
Protein phosphorylation plays a crucial role in mitogenic signal transduction and regulation of cell growth and differentiation. Dual specificity protein phosphatase 23 (DUSP23) or VHZ mediates dephosphorylation of phospho-tyrosyl (pTyr) and phospho-seryl/threonyl (pSer/pThr) residues in specific proteins. In vitro, it can dephosphorylate p44ERK1 but not p54SAPK-beta and enhance activation of c-Jun N-terminal kinase (JNK) and p38. Human VHZ, the smallest of the catalytically active protein-tyrosine phosphatases (PTP) reported to date (150 residues), is a class I Cys-based PTP and bears the distinctive active site signature motif HCXXGXXRS(T). We present the crystal structure of VHZ determined at 1.93A resolution. The polypeptide chain adopts the typical alphabetaalpha PTP fold, giving rise to a shallow active site cleft that supports dual phosphorylated substrate specificity. Within our crystals, the Thr-135-Tyr-136 from a symmetry-related molecule bind in the active site with a malate ion, where they mimic the phosphorylated TY motif of the MAPK activation loop in an enzyme-substrate/product complex. Analyses of intermolecular interactions between the enzyme and this pseudo substrate/product along with functional analysis of Phe-66, Leu-97, and Phe-99 residues provide insights into the mechanism of substrate binding and catalysis in VHZ. 相似文献
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Bacillus cereus Hemolysin BL enterotoxin, a ternary complex of three proteins, is the causative agent of food poisoning and requires all three components for virulence. The X-ray structure of the binding domain of HBL suggests that it may form a pore similar to other soluble channel forming proteins. A putative pathway of pore formation is discussed. 相似文献
78.
Zhang Z Zhou R Sauder JM Tonge PJ Burley SK Swaminathan S 《Journal of molecular biology》2011,406(2):313-324
Fatty acyl-AMP ligase (FAAL) is a new member of a family of adenylate-forming enzymes that were recently discovered in Mycobacterium tuberculosis. They are similar in sequence to fatty acyl-coenzyme A (CoA) ligases (FACLs). However, while FACLs perform a two-step catalytic reaction, AMP ligation followed by CoA ligation using ATP and CoA as cofactors, FAALs produce only the acyl adenylate and are unable to perform the second step. We report X-ray crystal structures of full-length FAAL from Escherichia coli (EcFAAL) and FAAL from Legionella pneumophila (LpFAAL) bound to acyl adenylate, determined at resolution limits of 3.0 and 1.85 Å, respectively. The structures share a larger N-terminal domain and a smaller C-terminal domain, which together resemble the previously determined structures of FAAL and FACL proteins. Our two structures occur in quite different conformations. EcFAAL adopts the adenylate-forming conformation typical of FACLs, whereas LpFAAL exhibits a unique intermediate conformation. Both EcFAAL and LpFAAL have insertion motifs that distinguish them from the FACLs. Structures of EcFAAL and LpFAAL reveal detailed interactions between this insertion motif and the interdomain hinge region and with the C-terminal domain. We suggest that the insertion motifs support sufficient interdomain motions to allow substrate binding and product release during acyl adenylate formation, but they preclude CoA binding, thereby preventing CoA ligation. 相似文献
79.
A new method for measuring maximum stomach or digestive tract volume of fish incorporates air injection at constant pressure with water displacement to measure directly the internal volume of a stomach or analogous structure. The method was tested with coho salmon, Oncorhynchus kisutch (Walbaum), which has a true stomach, and northern squawfish, Ptychocheilus oregonensis (Richardson), which has a modified foregut as a functional analogue. Both species were collected during July-October 1987 from the Columbia River, U.S.A. Relationships between fish weight (= volume) and maximum volume of the digestive organ were best fitted for coho salmon by an allometric model and for northern squawfish by an exponential model. Least squares regression analysis of individual measurements showed less variability in the volume of coho salmon stomachs ( R2 = 0.85) than in the total digestive tracts ( R2 = 0.55) and foreguts ( R2 = 0.61) of northern squawfish, relative to fish size. Compared to previous methods, the new technique has the advantage of accurately measuring the internal volume of a wide range of digestive organ shapes and sizes. 相似文献
80.
Darwin first hypothesized that bright colors and elaborate ornamentation of male animals evolved in response to the "aesthetic" mate preferences of females. By this reasoning, potentially costly male secondary sexual traits may evolve not in response to selection for demonstration of vigor but, rather, in response to latent, nonfunctional preferences by females. Recent comparative evidence for this phenomenon is equivocal. Here we present experimental evidence that two avian species from a lineage devoid of crested species have mate preferences for opposite sex conspecifics wearing artificial white crests. Other colors of crests that have been studied are not preferred. Preferences for white crests did not diminish over the longest experimental interval (12 wk). These results are additional powerful evidence for highly structured aesthetic mate preferences in estrildine finches. Sex differences in the expression of preferences, and the widespread occurrence of facial ornamentation in birds, suggest that the preference "structure" is influenced by the central nervous system. We hypothesize that aesthetic preferences are a potent force in the early evolution of sexually selected traits, and that "indicator" traits evolve secondarily from traits initially favored by aesthetic preferences. 相似文献