A urea channel from Bacillus cereus reveals a novel hexameric structure

The Biochemical Journal
Gerard H M HuysmansStephen A Baldwin

Abstract

Urea is exploited as a nitrogen source by bacteria, and its breakdown products, ammonia and bicarbonate, are employed to counteract stomach acidity in pathogens such as Helicobacter pylori. Uptake in the latter is mediated by UreI, a UAC (urea amide channel) family member. In the present paper, we describe the structure and function of UACBc, a homologue from Bacillus cereus. The purified channel was found to be permeable not only to urea, but also to other small amides. CD and IR spectroscopy revealed a structure comprising mainly α-helices, oriented approximately perpendicular to the membrane. Consistent with this finding, site-directed fluorescent labelling indicated the presence of seven TM (transmembrane) helices, with a cytoplasmic C-terminus. In detergent, UACBc exists largely as a hexamer, as demonstrated by both cross-linking and size-exclusion chromatography. A 9 Å (1 Å=0.1 nm) resolution projection map obtained by cryo-electron microscopy of two-dimensional crystals shows that the six protomers are arranged in a planar hexameric ring. Each exhibits six density features attributable to TM helices, surrounding a putative central channel, while an additional helix is peripherally located. Bioinformatic analyses allowed ...Continue Reading

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Citations

Dec 7, 2013·Nature Communications·Reginald McNultyMartin B Ulmschneider
Jun 23, 2015·Molecular Membrane Biology·Tony MageeStephen Muench
Mar 18, 2016·Journal of Phycology·Ramon TerradoConnie Lovejoy
Oct 20, 2018·The Journal of Biological Chemistry·Pengcheng SunDong Deng

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