Figure 1.

Scheme of the proteolytic events that activate the aerobactin-induced Iut CSS system of P. putida. (A) The two proteins of the system, the IutA CSS receptor and the IutY sigma/anti-sigma hybrid protein are shown. In the absence of the siderophore, the sigma domain of IutY is inactive. (B) Binding of ferric-aerobactin to IutA generates a signal that, by analogy with other CSS systems, is likely transmitted to IutY by the signaling domain of IutA (dark gray ball). This triggers the proteolytic cleavage of the anti-sigma C-domain of IutY by the sequential action of the Prc and the RseP proteases. The resulting σ^IutY protein domain can then interact with the RNAP and initiates expression of the iutA gene. OM, outer membrane; CM, cytoplasmic membrane. Adapted from Bastiaansen et al. (2014) and Llamas et al. (2014).