Protein phosphorylation plays a central role in signal transduction in bacteria. However, separation and detection of the phosphorylated protein from its nonphosphorylated form remain challenging. Here we describe a method to detect phosphorylation of the Bordetella pertussis response regulator BvgA, which is phosphorylated at an aspartate residue (Boulanger et al., 2013). This method is based on the proprietary adduct, Phos-tagTM, a dinuclear metal complex, which together with Zn2+ or Mn2+, forms a complex with a phosphomonoesterdianion, such as the phosphorylated aspartate of a response regulator (Barbieri and Stock, 2008; Kinoshita and Kinoshita-Kikuta, 2011). For in vivo detection, B. pertussis cells are lysed in mild formic acid at 4 °C to minimize the disruption of the phospho-aspartate bond, and the phosphorylated BvgA is separated from its nonphosphorylated form by electrophoresis (SDS-PAGE) containing Phos-tagTM. Both forms of BvgA are subsequently detected by Western Blot analysis. Quantification of the level of phosphorylated BvgA formed after treatment with acetyl phosphate in vitro is also easily accomplished. Thus, this technique allows one to readily assess the levels of BvgA phosphorylation in B. pertussis and in E. coli under different laboratory conditions in vivo or after phosphorylation under varying reaction conditions in vitro (this research was supported in part by the Intramural Research Program of the NIH, NIDDK).
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