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Co(II)-detection does not follow K_co(^II) gradient: channelling in Co(II)-sensing

Lookup NU author(s): Carl Patterson, Dr Rafael Pernil-Garcia, Dr Sam Dainty, Dr Andrew Foster, Professor Nigel Robinson

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Abstract

The MerR-like transcriptional activator CoaR detects surplus Co(II) to regulate Co(II) efflux in a cyanobacterium. This organism also has cytosolic metal-sensors from three further families represented by Zn(II)-sensors ZiaR and Zur plus Ni(II)-sensor InrS. Here we discover by competition with Fura-2 that CoaR has K-Co(II) weaker than 7 x 10(-8) M, which is weaker than ZiaR, Zur and InrS (K-Co(II) = 6.94 +/- 1.3 x 10(-10) M; 4.56 +/- 0.16 x 10(-10) M; and 7.69 +/- 1.1 x 10(-9) M respectively). K-Co(II) for CoaR is also weak in the CoaR-DNA adduct. Further, Co(II) promotes DNA-dissociation by ZiaR and DNA-association by Zur in vitro in a manner analogous to Zn(II), as monitored by fluorescence anisotropy. After 48 h exposure to maximum non-inhibitory [Co(II)], CoaR responds in vivo yet the two Zn(II)-sensors do not, despite their tighter K-Co(II) and despite Co(II) triggering allostery in ZiaR and Zur in vitro. These data imply that the two Zn(II) sensors fail to respond because they fail to gain access to Co(II) under these conditions in vivo. Several lines of evidence suggest that CoaR is membrane associated via a domain with sequence similarity to precorrin isomerase, an enzyme of vitamin B-12 biosynthesis. Moreover, site directed mutagenesis reveals that transcriptional activation requires CoaR residues that are predicted to form hydrogen bonds to a tetrapyrrole. The Co(II)-requiring vitamin B-12 biosynthetic pathway is also membrane associated suggesting putative mechanisms by which Co(II)-containing tetrapyrroles and/or Co(II) ions are channelled to CoaR.

Publication metadata

Author(s): Patterson CJ, Pernil R, Dainty SJ, Chakrabarti B, Henry CE, Money VA, Foster AW, Robinson NJ

Publication type: Article

Publication status: Published

Journal: Metallomics

Year: 2013

Volume: 5

Issue: 4

Pages: 352-362

Print publication date: 01/04/2013

Online publication date: 31/01/2013

Acceptance date: 29/01/2013

ISSN (print): 1756-5901

ISSN (electronic): 1756-591X

Publisher: RSC Publications

URL: http://dx.doi.org/10.1039/c3mt20241k

DOI: 10.1039/c3mt20241k

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