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Instruments / Technical Area	Publication Details	Published	Actions
	Crystal Structure of the Acid Induced Arginine Decarboxylase from Escherichia coli: Reversible Decamer Assembly Controls Enzyme Activity Juni Andrell , Matthew Hicks , Tracy Palmer , Liz Carpenter , So Iwata , Megan Maher Biochemistry DOI: 10.1139/O09-182 PMID: 20453931 Diamond Proposal Number(s): [316] Show Abstract ▼ Abstract: Enteric bacteria such as Escherichia coli have acquired a wide array of acid stress response systems to counteract the extreme acidity encountered when invading the host's digestive or urinary tracts. These acid stress response systems are both enzyme and chaperone based. The 3 main enzyme-based acid resistance pathways are glutamate-, arginine-, and lysine-decarboxylase pathways. They are under a complex regulatory network allowing the bacteria to fine tune its response to the external environment. HdeA and HdeB are the main chaperones involved in acid stress response. The decarboxylase systems are also found in Vibrio cholera, Vibrio vulnifus, Shigella flexneri. and Salmonella typhimurium, although some differences exist in their functional mechanism and regulation.	Mar 2009
NONE-No attached Diamond beamline	Thioredoxin A active-site mutants form mixed disulfide dimers that resemble enzyme-substrate reaction intermediates. Thijs R. H. M. Kouwen , Rianne Schrijver , Jean-yves F. Dubois , Megan J. Maher , Elizabeth P. Carpenter , Juni Andrell , So Iwata , Jan Maarten Van Dijl Journal Of Molecular Biology 379 (3), 520-34 DOI: 10.1016/j.jmb.2008.03.077 PMID: 18455736 Show Abstract ▼ Abstract: Thioredoxin functions in nearly all organisms as the major thiol-disulfide oxidoreductase within the cytosol. Its prime purpose is to maintain cysteine-containing proteins in the reduced state by converting intramolecular disulfide bonds into dithiols in a disulfide exchange reaction. Thioredoxin has been reported to contribute to a wide variety of physiological functions by interacting with specific sets of substrates in different cell types. To investigate the function of the essential thioredoxin A (TrxA) in the low-GC Gram-positive bacterium Bacillus subtilis, we purified wild-type TrxA and three mutant TrxA proteins that lack either one or both of the two cysteine residues in the CxxC active site. The pure proteins were used for substrate-binding studies known as "mixed disulfide fishing" in which covalent disulfide-bonded reaction intermediates can be visualized. An unprecedented finding is that both active-site cysteine residues can form mixed disulfides with substrate proteins when the other active-site cysteine is absent, but only the N-terminal active-site cysteine forms stable interactions. A second novelty is that both single-cysteine mutant TrxA proteins form stable homodimers due to thiol oxidation of the remaining active-site cysteine residue. To investigate whether these dimers resemble mixed enzyme-substrate disulfides, the structure of the most abundant dimer, C32S, was characterized by X-ray crystallography. This yielded a high-resolution (1.5A) X-ray crystallographic structure of a thioredoxin homodimer from a low-GC Gram-positive bacterium. The C32S TrxA dimer can be regarded as a mixed disulfide reaction intermediate of thioredoxin, which reveals the diversity of thioredoxin/substrate-binding modes.	Jun 2008

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