Membrane Sequestration of PII Proteins and Nitrogenase Regulation in the photosynthetic bacterium Rhodobacter capsulatus

Département de microbiologie et immunologie, Université de Montréal, Montréal, Québec H3C 3J7 Canada, Institut für Molekulare Enzymtechnologie, Heinrich-Heine-Univertität Düsseldorf, Forschungszentrum Jülich, 52426 Jülich, Germany, Ruhr-Universität Bochum, Lehrstuhl für Biologie der Mikroorganismen, D-44780 Bochum, Germany

^* To whom correspondence should be addressed. Email: patrick.hallenbeck{at}umontreal.ca.

	Abstract

Both Rhodobacter capsulatus PII homologs, GlnB and GlnK were found to be necessary for the proper regulation of nitrogenase activity and modification in response to an ammonium shock. As previously reported for several other bacteria, ammonium addition triggered the AmtB-dependent association of GlnK with the R. capsulatus membrane. Native PAGE analysis indicates that the modification/demodification of one PII homolog is aberrant in the absence of the other. In a glnK mutant, more GlnB was found to be membrane associated under these conditions. In a glnB mutant, GlnK fails to be significantly sequestered by AmtB even though it appears to be fully deuridylylated. Additionally, the ammonium-induced enhanced sequestration by AmtB of the unmodifiable GlnK variant, GlnK-Y51F, follows the wild-type GlnK pattern with a high level in the cytoplasm without the addition of ammonium and an increased level in the membrane fraction after ammonium treatment. These results suggest that factors other than PII modification are driving its association with AmtB in the membrane in R. capsulatus.