Globin coupled sensors (GCSs) are heme-based proteins that can regulate their output domain activity in response to O2 binding to their sensor globin domain. Previous characterization of GCSs has focused on elucidating the signal transduction mechanism from the globin domain to the output domain in response to binding O2. We have recently identified a bifunctional GCS from Paenibacillus dendritiformis (PdGCS) that contains a diguanylate cyclase and c-di-GMP phosphodiesterase domain. Surprisingly, PdGCS was demonstrated to exhibit a redox potential of 275 mV vs. SHE, which is considerably higher than typical O2 binding heme proteins (myoglobin = 58 mV vs. SHE). Site-directed mutagenesis of a heme-edge histidine residue to an alanine results in a 200 mV decrease in its redox potential, identifying a role for the histidine in modulating PdGCS heme electronics. Dissociation of O2 from the heme was investigated to further probe heme properties; the O2 dissociation of PdGCS exhibits bi-exponential kinetics of k1 = 16.93 s-1 and k2 = 106.4 s-1, suggesting that PdGCS has multiple conformations of the heme pocket. These findings provide insight into molecular interactions that regulate PdGCS O2 sensing and redox potential, as well as its signaling.

Unusual heme properties of a bifunctional O2-dependent globin coupled sensor

2019 Spring National Meeting

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