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Crystal structure of B acillus anthracis virulence regulator AtxA and effects of phosphorylated histidines on multimerization and activity
Author(s) -
Hammerstrom Troy G.,
Horton Lori B.,
Swick Michelle C.,
Joachimiak Andrzej,
Osipiuk Jerzy,
Koehler Theresa M.
Publication year - 2015
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 - 10.1111/mmi.12867
Subject(s) - phosphorylation , anthrax toxin , virulence , biology , biochemistry , operon , chemistry , phosphotransferase , dimer , microbiology and biotechnology , gene , escherichia coli , recombinant dna , fusion protein , organic chemistry
Summary The B acillus anthracis virulence regulator AtxA controls transcription of the anthrax toxin genes and capsule biosynthetic operon. AtxA activity is elevated during growth in media containing glucose and CO 2 /bicarbonate, and there is a positive correlation between the CO 2 /bicarbonate signal, AtxA activity and homomultimerization. AtxA activity is also affected by phosphorylation at specific histidines. We show that AtxA crystallizes as a dimer. Distinct folds associated with predicted DNA ‐binding domains ( HTH 1 and HTH 2) and phosphoenolpyruvate: carbohydrate phosphotransferase system‐regulated domains ( PRD 1 and PRD 2) are apparent. We tested AtxA variants containing single and double phosphomimetic ( H is→ A sp) and phosphoablative ( H is→ A la) amino acid changes for activity in B . anthracis cultures and for protein–protein interactions in cell lysates. Reduced activity of AtxA H199A, lack of multimerization and activity of AtxA H379D variants, and predicted structural changes associated with phosphorylation support a model for control of AtxA function. We propose that (i) in the AtxA dimer, phosphorylation of H 199 in PRD 1 affects HTH 2 positioning, influencing DNA ‐binding; and (ii) phosphorylation of H 379 in PRD 2 disrupts dimer formation. The AtxA structure is the first reported high‐resolution full‐length structure of a PRD ‐containing regulator, and can serve as a model for proteins of this family, especially those that link virulence to bacterial metabolism.