Nitrophorin
Nitrophorins are
The salivary nitrophorin from the
The crystal structures of several nitrophorin complexes are known. The Rhodnius prolixus nitrophorin structures reveal lipocalin-like eight-stranded β-barrel, three α-helices and two disulfide bonds, with heme inserted into one end of the barrel. Members of the lipocalin family are known to bind a variety of small hydrophobic ligands, including biliverdin, in a similar fashion. The heme iron is ligated to histidine residue (His-59). The position of His-59 is restrained through water-mediated hydrogen bond to the carboxylate of aspartic acid residue (Asp-70). The His-59–Fe bond is bent ~15° out of the imidazole plane. Asp-70 forms an unusual hydrogen bond with one of the heme propionates, suggesting the residue has an altered pKa. In NP1-histamine structure, the planes of His-59 and histamine imidazole rings lie in an arrangement almost identical to that found in oxidized cytochrome b5.
The fold of nitrophorin from Cimex lectularius consists of central 11-stranded β-sandwich and seven peripheral α-helices. The heme is positioned between β-sheet and an α-helix, with heme iron ligated to cysteinate residue. NO can bind both to heme Fe3+ and to proximal Cys-60 ligand causing reversible S-nitrosylation.
References
- PMID 15598503.
External links and further reading
- Montfort, W.R., Weichsel, A. and Andersen, J.F. (2000). "Nitrophorins and related antihemostatic lipocalins from Rhodnius prolixus and other blood-sucking arthropods". Biochim. Biophys. Acta. 1482 (1–2): 110–118. PMID 11058753.)
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: CS1 maint: multiple names: authors list (link - Valenzuela, J.G. & Ribeiro, J.M.C. (1998). "Purification and cloning of the salivary nitrophorin from the hemipteran Cimex lectularius". J. Exp. Med. 201 (Pt 18): 2659–2664. PMID 9716517.
- Weichsel, A., Maes, E.M., Andersen, J.F., Valenzuela, J.G., Shokhireva, T.Kh., Walker, F.A. and Montfort, W.R. (2005). "Heme-assisted S-nitrosation of a proximal thiolate in a nitric oxide transport protein". Proc. Natl. Acad. Sci. USA. 102 (3): 594–599. PMID 15637157.)
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: CS1 maint: multiple names: authors list (link - PDB: 1NP1 - X-ray structure of Rhodnius prolixus nitrophorin 1 complexed with histamine and PO43−
- PDB: 1Y21 - X-ray structure of Cimex lectularius nitrophorin in complex with NO
- Montfort Lab - Nitrophorin research @ University of Arizona, Tucson, USA