Probing the Local Electronic and Geometric Properties of the Heme Iron Center in a H-NOX Domain

Journal Article · Sat Dec 31 04:00:00 EST 2011 · Journal of Inorganic Biochemistry

DOI:https://doi.org/10.1016/j.jinorgbio.2011.03.002· OSTI ID:1042011

Dai, Z; Boon, E

Heme-Nitric oxide and/or OXygen binding (H-NOX) proteins are a family of diatomic gas binding hemoproteins that have attracted intense research interest. Here we employ X-ray absorption near-edge structure (XANES) spectroscopy to study the nitric oxide (NO) binding site of H-NOX. This is the first time this technique has been utilized to examine the NO/H-NOX signaling pathway. XANES spectra of wildtype and a point mutant (proline 115 to alanine, P115A) of the H-NOX domain from Thermoanaerobacter tengcongensis (Tt H-NOX) were obtained and analyzed for ferrous and ferric complexes of the protein. This work provides specific structural characterization of the solution state of several Tt H-NOX ferrous complexes (- unligated, - NO, and - CO) that were previously unavailable. Our iron K-edges indicate effective charge on the iron center in the various complexes and report on the electronic environment of heme iron. We analyzed the ligand field indicator ratio (LFIR), which is extracted from XANES spectra, for each complex, providing an understanding of ligand field strength, spin state of the central iron, movement of the iron atom upon ligation, and ligand binding properties. In particular, our LFIRs indicate that the heme iron is dramatically displaced towards the distal pocket during ligand binding. Based on these results, we propose that iron displacement towards the distal heme pocket is an essential step in signal initiation in H-NOX proteins. This provides a mechanistic link between ligand binding and the changes in heme and protein conformation that have been observed for H-NOX family members during signaling.

• Research Organization: BROOKHAVEN NATIONAL LABORATORY (BNL)
• Sponsoring Organization: USDOE SC OFFICE OF SCIENCE (SC)
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 1042011
• Report Number(s): BNL--97689-2012-JA
• Journal Information: Journal of Inorganic Biochemistry, Journal Name: Journal of Inorganic Biochemistry Journal Issue: 6 Vol. 105; ISSN JIBIDJ; ISSN 0162-0134
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
60 APPLIED LIFE SCIENCES
ABSORPTION
ATOMS
EFFECTIVE CHARGE
HEME
IRON
MUTANTS
NITRIC OXIDE
OXIDES
OXYGEN
PROLINE
PROTEINS
SPECTRA
SPECTROSCOPY
SPIN