| Abstract
| - The phosphodiesterase A1 protein of Acetobacter xylinum,AxPDEA1, is a key regulator ofbacterial cellulose synthesis. This phosphodiesterase linearizes cyclic bis(3‘→5‘)diguanylic acid, an allostericactivator of the bacterial cellulose synthase, to the ineffectual pGpG. Here we show that AxPDEA1 containsheme and is regulated by reversible binding of O2 to the heme. Apo-AxPDEA1 has less than 2% of thephosphodiesterase activity of holo-AxPDEA1, and reconstitution with hemin restores full activity. O2regulation is due to deoxyheme being a better activator than oxyheme. AxPDEA1 is homologous to theEscherichia coli direct oxygen sensor protein, EcDos, over its entire length and is homologous to theFixL histidine kinases over only a heme-binding PAS domain. The properties of the heme-binding domainof AxPDEA1 are significantly different from those of other O2-responsive heme-based sensors. The rateof AxPDEA1 autoxidation (half-life > 12 h) is the slowest observed so far for this type of heme proteinfold. The O2 affinity of AxPDEA1 (Kd ∼ 10 μM) is comparable to that of EcDos, but the rate constantsfor O2 association (kon = 6.6 μM-1 s-1) and dissociation (koff = 77 s-1) are 2000 times higher. Our resultsillustrate the versality of signal transduction mechanisms for the heme-PAS class of O2 sensors and providethe first example of O2 regulation of a second messenger.
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