Characterization of BLUF-photoreceptors present in Acinetobacter nosocomialis.

Abstract

Acinetobacter nosocomialis is a Gram-negative opportunistic pathogen, whose ability to cause disease in humans is well recognized. Blue light has been shown to modulate important physiological traits related to persistence and virulence in this microorganism. In this work, we characterized the three Blue Light sensing Using FAD (BLUF) domain-containing proteins encoded in the A. nosocomialis genome, which account for the only "traditional" light sensors present in this microorganism. By focusing on a light-modulated bacterial process such as motility, the temperature dependence of light regulation was studied, as well as the expression pattern and spectroscopic characteristics of the different A. nosocomialis BLUFs. Our results show that the three BLUF-containing proteins encode active photoreceptors, despite only two of them are stable in the light-regulatory temperature range when expressed recombinantly. In vivo, only the A. baumanniis ortholog AnBLUF65 is expressed, which is active in a temperature range from 15 {degrees}C to 37 {degrees}C. In turn, AnBLUF46 is an active photoreceptor between 15 {degrees}C to 32 {degrees}C in vitro, but is not expressed in A. nosocomialis in the conditions tested. Intra-protein interactions were analyzed using 3D models built based on A. baumannis photoreceptor, to support spectroscopic data and profile intra-protein residue interactions. A general scheme is presented on how hydrophobic/aromatic interactions may contribute to the stability of dark/light- adapted states, indicating the importance of these interactions in BLUF photoreceptors.