Probing The Chemotaxis Periplasmic Sensor Domains from G. sulfurreducens by Combined Resonance Raman and Molecular Dynamic Approaches: NO and CO Sensing

T CATARINO; M PESSANHA; ARIEL DE CANDIA; Z GOUVEIA; AP FERNÁNDEZ; P R POKKULURI; DANIEL H MURGIDA; MARCELO A MARTI; SMILJA TODOROVIC; C A SALGUEIRO

JOURNAL OF PHYSICAL CHEMISTRY B - (Print)

AMER CHEMICAL SOC

Año: 2010 p. 11251 - 11260

1520-6106

The periplasmic sensor domains encoded by genes gsu0582 and gsu0935 are part of methyl acceptingchemotaxis proteins in the bacterium Geobacter sulfurreducens (Gs). The sensor domains of these proteinscontain a heme-c prosthetic group and a PAS-like fold as revealed by their crystal structures. Biophysicalstudies of the two domains showed that nitric oxide (NO) binds to the heme in both the ferric and ferrousforms, whereas carbon monoxide (CO) binds only to the reduced form. In order to address these exogenousmolecules as possible physiological ligands, binding studies and resonance Raman (RR) spectroscopiccharacterization of the respective CO and NO adducts were performed in this work. In the absence of exogenousligands, typical RR frequencies of five-coordinated (5c) high-spin and six-coordinated (6c) low-spin specieswere observed in the oxidized form. In the reduced state, only frequencies corresponding to the latter weredetected. In both sensors, CO binding yields 6c low-spin adducts by replacing the endogenous distal ligand.The binding of NO by the two proteins causes partial disruption of the proximal Fe-His bond, as revealed bythe RR fingerprint features of 5cFe-NO and 6cNO-Fe-His species. The measured CO and NO dissociationconstants of ferrous GSU0582 and GSU0935 sensors reveal that both proteins have high and similar affinitytoward these molecules (Kd ≈ 0.04-0.08 µM). On the contrary, in the ferric form, sensor GSU0582 showeda much higher affinity for NO (Kd ≈ 0.3 µM for GSU0582 versus 17 µM for GSU0935). Molecular dynamicscalculations revealed a more open heme pocket in GSU0935, which could account for the different affinitiesfor NO. Taken together, spectroscopic data and MD calculations revealed subtle differences in the bindingproperties and structural features of formed CO and NO adducts, but also indicated a possibility that a (5c)high-spin/(6c) low-spin redox-linked equilibrium could drive the physiological sensing of Gs cells.