Nitric Oxide Synthases of Bacteria - and Other Unicellular Organisms

ABSTRACT

The defining feature of a nitric oxide synthase (NOS) is a heme and pterin-binding oxygenase domain, and enzymes that possess this domain are found in animals and bacteria. While the roles of animal NOS in such processes as vasodilation, neurotransmission, and host defence are understandably important for multicellular life, they are meaningless in bacteria, which makes bacterial NOSs all the more interesting as objects of study. This review describes the structural similarities and differences between animal and bacterial NOS, and how such differences may influence the extent and duration of bacterial NO production, and, ultimately the roles of NO in microorganisms. Recent progress in defining the functions of bacterially-derived NO, notably in protection from various stresses and as a potential transcriptional regulator are described. Finally, an attempt is made to span the gap between animal and bacterial nitric oxide synthases by commenting on the search for examples of NOS in single-celled eukaryotes, where progress seems imminent.

Keywords:

Bacterial nitric oxide synthase, unicellular nitric oxide synthase, nitric oxide synthase structure and function.