1.
Structural Insight into H-NOX Gas Sensing and Cognate Signaling Protein Regulation.
Guo, Y, Marletta, MA
Chembiochem : a European journal of chemical biology. 2019;(1):7-19
Abstract
Heme-nitric oxide/oxygen binding (H-NOX) proteins are a family of gas-binding hemoproteins that bind diatomic gas ligands such as nitric oxide (NO) and oxygen (O2 ). In bacteria, H-NOXs are often associated with signaling partners, including histidine kinases (HKs), diguanylate cyclases (DGCs) or methyl-accepting chemotaxis proteins (MCPs), either as a stand-alone protein or as a domain of a larger polypeptide. H-NOXs regulate the activity of cognate signaling proteins through ligand-induced conformational changes in the H-NOX domain and protein/protein interactions between the H-NOX and the cognate signaling partner. This review summarizes recent progress toward deciphering the molecular mechanism of bacterial H-NOX activation and the subsequent regulation of H-NOX-associated cognate sensor proteins from a structural and biochemical point of view.
2.
Spectroscopic and Reactivity Comparisons between Nonheme Oxoiron(IV) and Oxoiron(V) Species Bearing the Same Ancillary Ligand.
Dantignana, V, Serrano-Plana, J, Draksharapu, A, Magallón, C, Banerjee, S, Fan, R, Gamba, I, Guo, Y, Que, L, Costas, M, et al
Journal of the American Chemical Society. 2019;(38):15078-15091
Abstract
This work directly compares the spectroscopic and reactivity properties of an oxoiron(IV) and an oxoiron(V) complex that are supported by the same neutral tetradentate N-based PyNMe3 ligand. A complete spectroscopic characterization of the oxoiron(IV) species (2) reveals that this compound exists as a mixture of two isomers. The reactivity of the thermodynamically more stable oxoiron(IV) isomer (2b) is directly compared to that exhibited by the previously reported 1e--oxidized analogue [FeV(O)(OAc)(PyNMe3)]2+ (3). Our data indicates that 2b is 4 to 5 orders of magnitude slower than 3 in hydrogen atom transfer (HAT) from C-H bonds. The origin of this huge difference lies in the strength of the O-H bond formed after HAT by the oxoiron unit, the O-H bond derived from 3 being about 20 kcal·mol-1 stronger than that from 2b. The estimated bond strength of the FeIVO-H bond of 100 kcal·mol-1 is very close to the reported values for highly active synthetic models of compound I of cytochrome P450. In addition, this comparative study provides direct experimental evidence that the lifetime of the carbon-centered radical that forms after the initial HAT by the high valent oxoiron complex depends on the oxidation state of the nascent Fe-OH complex. Complex 2b generates long-lived carbon-centered radicals that freely diffuse in solution, while 3 generates short-lived caged radicals that rapidly form product C-OH bonds, so only 3 engages in stereoretentive hydroxylation reactions. Thus, the oxidation state of the iron center modulates not only the rate of HAT but also the rate of ligand rebound.