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Instruments / Technical Area	Publication Details	Published	Actions
I24-Microfocus Macromolecular Crystallography	The Self-Assembly Mechanism for a Naphthalene-Dipeptide Leading to Hydrogelation Kyle Morris , Andrea Laybourn , David Elias , Matthew Hicks , David Elias , Louise Serpell , Dave Adams Journal Of The American Chemical Society DOI: 10.1021/la903694a PMID: 19921840 Diamond Proposal Number(s): [1234] Show Abstract ▼ Abstract: Suitably functionalized dipeptides have been shown to be effective hydrogelators. The design of the hydrogelators and the mechanism by which hydrogelation occurs are both currently not well understood. Here, we have utilized the hydrolysis of glucono-delta-lactone to gluconic acid as a means of adjusting the pH in a naphthalene-alanylvaline solution allowing the specific targeting of the final pH. In addition, this method allows the assembly process to be characterized. We show that assembly begins as charge is removed from the C-terminus of the dipeptide. The removal of charge allows lateral assembly of the molecules leading to pi-pi stacking (shown by CD) and beta-sheet formation (as shown by IR and X-ray fiber diffraction). This leads to the formation of fibrous structures. Electron microscopy reveals that thin fibers form initially, with low persistence length. Lateral association then occurs to give bundles of fibers with higher persistence length. This results in the initially weak hydrogel becoming stronger with time. The final mechanical properties of the hydrogels are very similar irrespective of the amount of GdL added; rather, the time taken to achieving the final gel is determined by the GdL concentration. However, differences are observed between the networks under strain, implying that the kinetics of assembly do impart different final materials' properties. Overall, this study provides detailed understanding of the assembly process that leads to hydrogelation.	Nov 2009
	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

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