Dynamical characterization of the Heme NO Oxygen binding (H-NOX) domain. Insight into soluble guanylate cyclase allosteric transition

LUCIANA CAPECE; DARIO A ESTRIN; MARCELO A. MARTI

BIOCHEMISTRY

ACS

Año: 2008 p. 9416 - 9427

0006-2960

ABSTRACT:    Since the discovery of soluble guanylate cyclase (sGC) as the mammalian receptor for nitricoxide (NO), numerous studies have been performed in order to understand how sGC transduces the NOsignal. However, the structural basis of sGC activation is still not completely elucidated. Spectroscopicand kinetic studies showed that the key step in the activation mechanism was the NO-induced breakingof the iron proximal histidine bond in the so-called 6c-NO to 5c-NO transition. The main breakthroughin the understanding of sGC activation mechanism came, however, from the elucidation of crystal structuresfor two different prokaryotic heme NO oxygen (HNOX) domains, which are homologues to the sGCheme domain. In this work we present computer simulation results of Thermoanaerobacter tencogensisHNOX that complement these structural studies, yielding molecular explanations to several poorlyunderstood properties of these proteins. Specifically, our results explain the differential ligand bindingpatterns of the HNOX domains according to the nature of proximal and distal residues. We also showthat the natural dynamics of these proteins is intimately related with the proposed conformational dependentactivation process, which involves mainly the RF 1 loop and the RA-RC distal subdomain. The resultsfrom the sGC models also support this view and suggest a key role for the RF 1 loop in the iron proximalhistidine bond breaking process and, therefore, in the sGC activation mechanism.