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A Bacterial Hemerythrin Domain Regulates the Activity of a Vibrio cholerae Diguanylate Cyclase
journal contribution
posted on 2012-10-30, 00:00 authored by Ruth A. Schaller, Syed Khalid Ali, Karl E. Klose, Donald M. KurtzThe first demonstrated example of a regulatory function
for a bacterial
hemerythrin (Bhr) domain is reported. Bhrs have a characteristic sequence
motif providing ligand residues for a type of non-heme diiron site
that is known to bind O2 and undergo autoxidation. The
amino acid sequence encoded by the VC1216 gene from Vibrio
cholerae O1 biovar El Tor str. N16961 contains an N-terminal
Bhr domain connected to a C-terminal domain characteristic of bacterial
diguanylate cyclases (DGCs) that catalyze formation of cyclic di-(3′,5′)-guanosine
monophosphate (c-di-GMP) from GTP. This protein, Vc Bhr-DGC, was found
to contain two tightly bound non-heme iron atoms per protein monomer.
The as-isolated protein showed the spectroscopic signatures of oxo/dicarboxylato-bridged
non-heme diferric sites of previously characterized Bhr domains. The
diiron site was capable of cycling between diferric and diferrous
forms, the latter of which was stable only under anaerobic conditions,
undergoing rapid autoxidation upon being exposed to air. Vc Bhr-DGC
showed approximately 10 times higher DGC activity in the diferrous
than in the diferric form. The level of intracellular c-di-GMP is
known to regulate biofilm formation in V. cholerae. The higher DGC activity of the diferrous Vc Bhr-DGC is consistent
with induction of biofilm formation in low-dioxygen environments.
The non-heme diiron cofactor in the Bhr domain thus represents an
alternative to heme or flavin for redox and/or diatomic gas sensing
and regulation of DGC activity.