Interaction with Membrane Lipids and Heme Ligand Binding Properties of Escherichia coli Flavohemoglobin

Abstract

Escherichia coli flavohemoglobin has been shown to be able to bind specifically unsaturated and/or cyclopropanated fatty acids with very high affinity. Unsaturated or cyclopropanated fatty acid binding results in a modification of the visible absorption spectrum of the ferric heme, corresponding to a transition from a pentacoordinated (typical of the ligand free protein) to a hexacoordinated, high spin, heme iron. In contrast, no detectable interaction has been observed with saturated fatty acid, saturated phospholipids, linear, cyclic, and aromatic hydrocarbons pointing out that the protein recognizes specifically double bonds in cis conformation within the hydrocarbon chain of the fatty acid molecule. Accordingly, as demonstrated in gel filtration experiments, flavohemoglobin is able to bind liposomes obtained from lipid extracts of E. coli membranes and eventually abstract phospholipids containing cis double bonds and/or cyclopropane rings along the acyl chains. The presence of a protein bound lipid strongly affects the thermodynamic and kinetic properties of imidazole binding to the ferric protein and brings about significant modifications in the reactivity of the ferrous protein with oxygen and carbon monoxide. The effect of the bound lipid has been accounted for by a reaction scheme that involves the presence of two sites for the lipid/ligand recognition, namely, the heme iron and a non-heme site located in a loop region above the heme pocket.

Structural heterogeneity and ligand gating in ferric methanosarcina acetivorans protoglobin mutants

“…3), and on the strong hydrophobicity of the MaPgb distal site cavity [lined by Phe(G7)145, Ile(G11)149, Phe(E11)93, Phe(CD1)74, Val(B13)64, Val(E7)89, Trp(B9)60, and Ala(B10)61], we propose that the unidentified heme-bound ligand is a small cyclic, possibly aromatic, compound. About the binding of uncommon heme ligands, it is worth noting that Escherichia coli flavohemoglobin and Vitreoscilla hemoglobin that host hydrophobic distal cavities [lined by Leu(E11), Phe(B9), and Tyr(B10)] have been reported to bind phospholipids and to interact efficiently with the phospholipid bilayer (9,10). To provide first clues about the nature of the unknown ligand, we collected absorption spectra on the Tyr(B10)61 ?…”

Role of an Inducible Single-Domain Hemoglobin in Mediating Resistance to Nitric Oxide and Nitrosative Stress in Campylobacter jejuni and Campylobacter coli

“…Under anaerobic conditions, in the absence of Hmp activity, the flavorubredoxin serves as an oxygen-independent NO reductase (19). Hmp may also function to repair NO-damaged lipid membranes, since the purified protein has recently been shown to possess both alkyl hydroperoxide reductase activity and lipid-binding properties (3,4). However, whether these activities are physiologically relevant has not yet been confirmed by in vivo studies.…”

A Membrane-bound Hemoglobin from Gills of the Green Shore Crab Carcinus maenas

“…A Hb in the cell membrane is unprecedented among eukaryotes. However, an association of Hb with membrane lipids has already been found in prokaryotes (43)(44)(45)(46)(47). For example, Vitreoscilla Hb is concentrated adjacent to the cytosolic side of the cell membrane (45).…”

“…It has been demonstrated that the active site of Vitreoscilla Hb interact with membrane lipids (46). Likewise, E. coli flavohemoglobin is able to bind to lipid extracts of E. coli membranes (43,47). These bacterial Hbs may actually provide hints to the function of CmaHb.…”