van Heeswijk, Wally C., Wen, Daying, Clancy, Paula, Jaggi, Rene, Ollis, David L., Westerhoff, Hans V., and Vasudevan, Subhash G. (2000) The Escherichia coli signal transducers PII (GlnB) and GlnK form heterotrimers in vivo: fine tuning the nitrogen signal cascade. National Academy of Sciences. Proceedings, 97 (8). pp. 3942-3947.

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Abstract

The PII protein is Escherichia coli's cognate transducer of the nitrogen signal to the NRII (NtrB)/NRI (NtrC) two-component system and to adenylyltransferase. Through these two routes, PII regulates both amount and activity of glutamine synthetase. GlnK is the recently discovered paralogue of PII, with a similar trimeric x-ray structure. Here we show that PII and GlnK form heterotrimers, in E. coli grown in nitrogen-poor medium. In vitro, fully uridylylated heterotrimers of the two proteins stimulated the deadenylylation activity of adenylyltransferase, albeit to a lower extent than homotrimeric PII-UMP. Fully uridylylated GlnK did not stimulate, or hardly stimulated, the deadenylylation activity. We propose that uridylylated PII/GlnK heterotrimers fine-regulate the activation of glutamine synthetase. The PII/GlnK couple is a first example of prokaryotic signal transducer that can form heterotrimers. Advantages of hetero-oligomer formation as molecular mechanism for fine-regulation of signal transduction are discussed.

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