Nitric oxide synthases in cyanobacteria: an overview on their occurrence, structure, and function

Abstract

Nitric oxide (NO) is an ancient signal molecule that plays a role in different physiological processes in cyanobacteria, together with organisms from Bacteria and other kingdoms. NOS enzymes appear in all three Domains of life: Archaea, Bacteria and Eukaryotes, pointing to an essential and conserved role of NO through evolution. Despite the fact that they have been identified for quite a long time, the characterization of NOS enzymes in cyanobacterial genomes is relatively recent. In this review we will outline the state-of-the-art on the enzymes NO synthases (NOS) in cyanobacteria. We will describe the occurrence of NOS in cyanobacterial genomes and the variety of NOS domains including novel arrangements. The identity of the pterin cofactor and Ca2+ requirement of the different NOS isoforms will be discussed. Two case studies of NOS function in the cyanobacteria Synechococcus PCC 7335 and Aphanizomenon flos-aquae will be presented. Finally, this chapter will also describe the chemistry of NO in biological systems and remarkable studies of the role of this molecule in the physiology of cyanobacteria. The NO action is an unexplored field that deserves more attention, particularly to provide a better understanding of the role of NOS enzymes in the physiology and NO homeostasis in cyanobacteria.