# Structure and dynamics of a multidomain nitric oxide synthase regulated by a C2 domain

## TL;DR

This paper reveals the structure and dynamic regulation of a multidomain nitric oxide synthase enzyme using cryo-electron microscopy.

## Contribution

The study provides the first detailed structural view of a full-length Synechococcus nitric oxide synthase with a regulatory C2 domain.

## Key findings

- The full-length Synechococcus NOS enzyme contains a regulatory C2 domain, a NOD module, and a pseudoglobin.
- Pterin binding is coupled to conformational changes in the oxygenase domain.
- The C2 domain moves over 85 angstroms to regulate either the NOS or NOD heme center.

## Abstract

Nitric oxide synthase (NOS) is a widely studied multidomain redox enzyme that produces the key signaling molecule and cytotoxic agent nitric oxide (NO) for functions that range from mammalian vasodilation to prokaryotic antibiotic resistance. NOS enzymes from metazoans and cyanobacteria rely on dynamic associations of their oxygenase and coupled diflavin reductase domains that have largely evaded detailed structural characterization. Cryo–electron microscopy studies of a representative dimeric six-domain Synechococcus NOS reveal the architecture of the full-length enzyme, which contains an unusual regulatory C2 domain, and additional nitric oxide dioxygenase (NOD) and pseudoglobin modules. Five distinct structural states depict how pterin binding couples to tight and loose oxygenase conformations and how the Ca2+-sensitive C2 domain moves over 85 angstroms to alternatively regulate either the NOS or NOD heme center. The extended carboxyl-terminal tail and its dynamic interactions highlight an added layer of regulation required by multidomain NOSs compared to other diflavin reductases.

syNOS is a highly dynamic multidomain oxidoreductase that harnesses a Ca2+-sensitive C2 domain to modulate activity.