Nitric Oxide Activation of Guanylate Cyclase Pushes the α1 Signaling Helix and the β1 Heme-binding Domain Closer to the Substrate-binding Site

Mareike Busker,Inga Neidhardt,Sönke Behrends

doi:10.1074/jbc.m113.504472

Abstract

The complete structure of the assembled domains of nitric oxide-sensitive guanylate cyclase (NOsGC) remains to be determined. It is also unknown how binding of NO to heme in guanylate cyclase is communicated to the catalytic domain. In the current study the conformational change of guanylate cyclase on activation by NO was studied using FRET. Endogenous tryptophan residues were used as donors, the substrate analog 2'-Mant-3'-dGTP as acceptor. The enzyme contains five tryptophan residues distributed evenly over all four functional domains. This provides a unique opportunity to detect the movement of the functional domains relative to the substrate-binding catalytic region. FRET measurements indicate that NO brings tryptophan 22 in the αB helix of the β1 heme NO binding domain and tryptophan 466 in the second short helix of the α1 coiled-coil domain closer to the catalytic domain. We propose that the respective domains act as a pair of tongs forcing the catalytic domain into the nitric oxide-activated conformation.

Highlights

IntroductionResults: FRET experiments show a movement of two tryptophans toward a fluorescent substrate
NO-induced conformational changes of guanylate cyclase were analyzed
We propose a model of NO activation where the movement of the ␣B helix of the ␤1 HNOX domain containing Trp-22 interacts directly with the catalytic domain, whereas the movement of the signaling helix containing His-105 is indirectly transmitted to the catalytic domain via the ␣1 PAS domain and ␣1 coiled-coil domain

Summary

Introduction

Results: FRET experiments show a movement of two tryptophans toward a fluorescent substrate. The complete structure of the assembled domains of nitric oxide-sensitive guanylate cyclase (NOsGC) remains to be determined. It is unknown how binding of NO to heme in guanylate cyclase is communicated to the catalytic domain. In the current study the conformational change of guanylate cyclase on activation by NO was studied using FRET. The enzyme contains five tryptophan residues distributed evenly over all four functional domains. This provides a unique opportunity to detect the movement of the functional domains relative to the substrate-binding catalytic region. We propose that the respective domains act as a pair of tongs forcing the catalytic domain into the nitric oxide-activated conformation

Results

Discussion

Conclusion