Nitrophorin 2, structure

General Information about Rhodnius Nitrophorin Structures... 

We have completed several structures each of NPl, NP2, and NP4 (31, 46 9, 110). These structures reveal the Rhodnius nitrophorins to have a fold dominated by an eight-stranded antiparallel beta-barrel, as shown in Fig. 15, and to rely on a remarkable ligand-induced conformational change for NO transport, described later. The structures confirm that the nitrophorins are completely unrelated to the globins, the only other heme-based gas transport proteins whose structures are known. Rather, their fold places them in the lipocalin family, for which several other examples are known (111-113). Our initial nitrophorin structure was of NPl and was determined using standard MIR and... 

The specific solvation of NO coordinated to Fe(III) and the resulting solvent reorganization upon NO dissociation (Fig. 3) finds some analogy with the nitrophorins, which are heme protein systems for NO transfer found in certain blood sucking insects. The crystal structure of one nitro-phorin, NP4, shows that binding of NO to the Fe(III) center leads to a collapse of the protein around the coordinated NO. The distal hemebinding pocket in nitrophorin NP4 is quite open to solvent in the absence of NO. It was postulated that collapse of the protein around the heme nitrosyl led to increased retention of bound NO at low pH (25). 

Structures of nitrophorin complexes with ammonia, histamine, cyanide, and nitric oxide have been obtained (31, 46-49, 110). These... 

NP2. In particular, Tyr82 flips from outside the protein in NP1/NP4, where it contacts bulk solvent, to inside the protein in NP2, where it hydrogen bonds to Glu55 (110). Thus, modeling the NP2 structure based on those of NPl and NP4, and, as is normally done, keeping the invariant residues structurally conserved, would lead to errors. Structures of protein families such as the nitrophorins therefore provide key information for the future improvement of structure prediction and structural genomics. 

Since the primary structure of a peptide determines the global fold of any protein, the amino acid sequence of a heme protein not only provides the ligands, but also establishes the heme environmental factors such as solvent and ion accessibility and local dielectric. The prevalent secondary structure element found in heme protein architectures is the a-helix however, it should be noted that p-sheet heme proteins are also known, such as the nitrophorin from Rhodnius prolixus (71) and flavocytochrome cellobiose dehydrogenase from Phanerochaete chrys-osporium (72). However, for the purpose of this review, we focus on the structures of cytochromes 6562 (73) and c (74) shown in Fig. 2, which are four-a-helix bundle protein architectures and lend themselves as resource structures for the development of de novo designs. 

E. M. Maes, "Structural Characterization of Iron and Copper Active Sites by Resonance Raman Spectroscopy Nitrophorin, Nitrite Reductase, and Iron-Sulfur Proteins, PhD. Dissertation, University of Houston, 2000. 

The structure of the bedbug Cimexlectulaiiu nitrophorin, called cNP, is also unique for a heme protein it consists of a... 

Nitrophorins (NP), nitric oxide (NO) transport proteins from the saliva of the bloodsucking insect Rhodniusprolixus that uses a ferric (Fe +) heme to deliver NO to the victims. Nitrophorins act as vasodilators and anti-platelet agents. At the tissue of the victim, the released NO molecule in the vicinity of the bite causes host signaling pathways that lead to vasodilation and reduced platelet aggregation. From crystal structure analysis of NPl and NP4 it follows that the nitrophorins have a unique hemopro-tein structure and are completely unlike the globins [J. M. C. Ribeiro et al.. Science 1993, 260, 539 J. F. Andersen et al.. Structure 1998, 6, 1315 E. M. Maes et al.. Biochemistry 2005, 44, 12690]. 

The structure above (determined by X-ray diffraction, PDB code 20FR) is that of a nitrophorin from Rhodnius prolixus complexed with NO at pH 5.6. The haem unit is bound... 

Cheng, M., Brookes, J.E., Montfort, W.R., Khalil, M. pH-dependent picosecond structural dynamics in the distal pocket of nitrophorin 4 investigated by 2D IR spectroscopy. J. Phys. Chem. B 117, 15804-15811 (2013)... 

The nitrophorins comprise a group of, NO transporting proteins found in the saliva of the blood sucking insect Rhodnius prolixus. ssNMR vras employed as an alternative method to gain structural insights on the precipitated protein by Varghese et Using isotopically la-... 

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