Three LOV-type Flavin-PAS Domains with Distinct Biochemical Properties in the Filamentous Cyanobacterium Anabaena sp. PCC 7120

Abstract

The PAS domain is one of the important signaling modules that monitor changes in light, redox potential, oxygen, and so on. Especially, LOV-type flavin-PAS domains of diverse proteins serve as a blue light sensor. There are many signal transduction proteins carrying PAS domains in the genome of a nitrogen-fixing heterocyst-forming cyanobacterium Anabaena sp. PCC 7120. From these proteins, we detected three novel LOV-type flavin-PAS proteins. Here, we expressed and purified these three LOV-type flavin-PAS domains from Escherichia coli. Two flavin-PAS domains that are conserved in a related cyanobacterium indeed bound FMN. They showed photoreduction similar to plant phototropins. However, one was fully photoreduced and dark reversion was very slow, whereas the other was slowly photoreduced and dark reversion was very fast. The third PAS domain that is unique to Anabaena 7120 did not bind flavin at all. Possible biological roles of these PAS domains will be discussed.