Metal ions are known to be delivered to a few metalloproteins by metallochaperones. Other metalloproteins acquire metals as complex cofactors. The remainder, representing perhaps two thirds of metalloproteins, are assumed to obtain metals from exchangeable cellular pools. For this final sub-set, the relative buffered intracellular concentrations of the various metal ions can dictate which metals are acquired. Genes whose products maintain these buffered metal-concentrations are controlled by metal-sensors from families of DNA-binding transcriptional-regulators including activators (eg MerR family), co-repressors (eg Fur family) and de-repressors (eg ArsR/SmtB, CopY plus CsoR/RcnR families). The primary and secondary metal-coordination spheres of the individual sensors determine which metals the sensors can bind and which metals can trigger the conformational changes that alter gene expression. However, this selectivity is insufficient to fully explain the spectrum of metals that each sensor is observed to detect inside cells. To further investigate such discernment of metals by cells we have completed the characterisation of a member from each family of metal-sensors represented in the genome of the cyanobacterium Synechocystis PCC 6803. Cobalt-sensing MerR-like activator CoaR and zinc-sensing SmtB-like de-repressor ZiaR were described previously: here we confirm zinc-dependent DNA-binding by a cyanobacterial Fur-like zinc-sensing co-repressor Zur, and discover an RcnR-like nickel-sensor plus its target gene encoding a nickel-efflux protein. Equilibrium dissociation constants for nickel have been measured for all four sensors by competition with Mag-Fura-2 and EGTA. Data will be presenteds which explain how the specific detection of nickel can become a shared function of a set of metal-sensors.

Specificity of metal-sensing in the set of DNA-binding transcriptional regulators of the cyanobacterium <i>Synechocystis</i> PCC 6803

243rd National Meeting (2012)

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Specificity of metal-sensing in the set of DNA-binding transcriptional regulators of the cyanobacterium Synechocystis PCC 6803