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Phosphorylation‐induced dimerization of the FixJ receiver domain
Author(s) -
Da Re Sandra,
Schumacher Jörg,
Rousseau Philippe,
Fourment Joëlle,
Ebel Christine,
Kahn Daniel
Publication year - 1999
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1999.01614.x
Subject(s) - biology , phosphorylation , biochemistry , activator (genetics) , sinorhizobium meliloti , transcription (linguistics) , microbiology and biotechnology , mutant , gene , linguistics , philosophy
The ‘two‐component’ transcriptional activator FixJ controls nitrogen fixation in Sinorhizobium meliloti . Phosphorylation of FixJ induces its dimerization, as evidenced by gel permeation chromatography and equilibrium sedimentation analysis. Phosphorylation‐induced dimerization is an intrinsic property of the isolated receiver domain FixJN. Accordingly, chemical phosphorylation of both FixJ and FixJN are second‐order reactions with respect to protein concentration. However, the second‐order phosphorylation constant is 44‐fold higher for FixJN than for FixJ. Therefore, the C‐terminal transcriptional activator domain FixJC inhibits the chemical phosphorylation of the receiver domain FixJN. Conversely, FixJN has been shown previously to inhibit FixJC activity ≈ 40‐fold, reflecting the interaction between FixJN and FixJC. Therefore, we propose that modulation of FixJ activity involves both its dimerization and the disruption of the interface between FixJN and FixJC, resulting in the opening of the protein structure. Alanine scanning mutagenesis of FixJN indicated that the FixJ~P dimerization interface involves Val‐91 and Lys‐95 in helix α4. Dimerization was required for high‐affinity binding to fixK promoter DNA.