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Abstract
In Escherichia coli, the CpxRA sensor regulator system is induced by a variety of
signals, including pH, osmolarity, metals and misfolded envelope proteins. Here, we
analyzed the effect of the folding defective maltose binding protein MalE219 on the
reconstituted Cpx signalling pathway in detail. Surprisingly, autokinase and phosphatase
activities of the reconstituted CpxA-6His protein remained unaffected, whereas phosphotransfer
to CpxR became activated by MalE219. Since stimulation occurred only in CpxA-containing
proteoliposomes, our data provide the first biochemical indication of allosteric stimulation
due to direct contact between MalE219 and the sensor kinase CpxA. Consequently, we
suggest that this direct interaction is a new mechanism enabling the Cpx pathway to
sense misfolded proteins.