1np4
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CRYSTAL STRUCTURE OF NITROPHORIN 4 FROM RHODNIUS PROLIXUS
OverviewOverview
BACKGROUND: Nitrophorins are nitric oxide (NO) transport proteins from the, saliva of blood-feeding insects, which act as vasodilators and, anti-platelet agents. Rhodnius prolixus, an insect that carries the, trypanosome that causes Chagas' disease, releases four NO-loaded, nitrophorins during blood feeding, whereupon the ligand is released into, the bloodstream or surrounding tissue of the host. Histamine, a signaling, molecule released by the host upon tissue damage, is tightly bound by the, nitrophorins; this may facilitate the release of NO and reduce, inflammation in the host. RESULTS: Recombinant nitrophorin 4 (NP4) was, expressed in Escherichia coli, reconstituted with heme, and found to bind, NO and histamine in a manner similar to that of the natural protein. The, crystal structure of NP4 revealed a lipocalin-like eight-stranded beta, barrel, with heme inserted into one end of the barrel. His59 ligates the, proximal site on the heme, a solvent molecule (NH3) ligates the distal, site, and three additional solvent molecules occupy the distal pocket., Buried in the protein interior are Glu55 and three solvent molecules. A, detailed comparison with other lipocalins suggests that NP4 is closely, related to the biliverdin-binding proteins from insects. CONCLUSIONS: The, nitrophorins have a unique hemoprotein structure and are completely unlike, the globins, the only other hemoproteins designed to transport dissolved, gases. Compared with the recently described structure of NP1, the NP4, structure is considerably higher resolution, confirms the unusual, placement of ionizable groups in the protein interior, and clarifies the, solvent arrangement in the distal pocket. It also provides a striking, example of structural homology where sequence homology is minimal.
About this StructureAbout this Structure
1NP4 is a Single protein structure of sequence from Rhodnius prolixus with HEM and NH3 as ligands. Full crystallographic information is available from OCA.
ReferenceReference
The crystal structure of nitrophorin 4 at 1.5 A resolution: transport of nitric oxide by a lipocalin-based heme protein., Andersen JF, Weichsel A, Balfour CA, Champagne DE, Montfort WR, Structure. 1998 Oct 15;6(10):1315-27. PMID:9782054
Page seeded by OCA on Tue Nov 20 22:26:54 2007