PDBsum entry 4hpc

Transport protein

PDB id: 4hpc

Contents

Protein chain

179 a.a.

Ligands

HEM-CYS

Waters ×176

PDB id:

4hpc

Name:

Transport protein

Title:

Crystal structure of nitrophorin 4 from rhodnius prolixus complexed with cysteine at ph 7.4

Structure:

Nitrophorin-4. Chain: a. Synonym: np4. Engineered: yes

Source:

Rhodnius prolixus. Triatomid bug. Organism_taxid: 13249. Expressed in: escherichia coli. Expression_system_taxid: 562.

Resolution:

1.40Å R-factor: 0.139 R-free: 0.169

Authors:

K.Nishikawa,H.Ogata,M.Knipp

Key ref:

C.He et al. (2013). Complexes of ferriheme nitrophorin 4 with low-molecular weight thiol(ate)s occurring in blood plasma. J Inorg Biochem, 122, 38-48. PubMed id: 23474537 DOI: 10.1016/j.jinorgbio.2013.01.012

Date:

23-Oct-12 Release date: 20-Mar-13

Protein chain

Q94734  (NP4_RHOPR) -  Nitrophorin-4 from Rhodnius prolixus

Seq: 205 a.a.

Struc: 179 a.a.

Enzyme reactions

• Enzyme class: E.C.1.7.6.1 - nitrite dismutase.
• Reaction: 3 nitrite + 2 H⁺ = 2 nitric oxide + nitrate + H2O
• Cofactor: Heme b

Heme b (Bound ligand (Het Group name = HEM) matches with 95.45% similarity)

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

reference

DOI no: 10.1016/j.jinorgbio.2013.01.012

J Inorg Biochem 122:38-48 (2013)

PubMed id: 23474537

Complexes of ferriheme nitrophorin 4 with low-molecular weight thiol(ate)s occurring in blood plasma.

C.He, K.Nishikawa, Ã.–.F.Erdem, E.Reijerse, H.Ogata, W.Lubitz, M.Knipp.

ABSTRACT

Nitrophorins are proteins occurring in the saliva of the blood-sucking insect Rhodnius prolixus to carry NO as a vasodilator and blood-coagulation inhibitor into the victim's tissue. It was suggested that the rate of NO release can be enhanced by the blood-plasma component L-cysteine [J.M.C.Ribeiro, Insect Biochem. Mol. Biol. 26 (1996) 899-905]. However, the mechanism of the reaction is not clear. In the attempt to exploit the reaction in detail, complexes of nitrophorin 4 (NP4) with the thiols 2-mercaptoethanol, L-cysteine, and L-homocysteine and with HS(-) were formed and characterized under anaerobic conditions using absorption spectroscopy, X-ray crystallography, and EPR spectroscopy. In contrast to met-myoglobin, which is reduced by L-cysteine, all four compounds form low-spin Fe(III) complexes with NP4. The weak equilibration constants (167-5200 M(-1)) neither support significant complexation nor the simple displacement of NO in vivo. Both amino acid based thiols form additional H-bonds with side chains of the heme pocket entry. Glutathione and L-methionine did not form a complex, indicating the specificity of the complexes with L-cysteine and L-homocysteine. Continuous wave EPR spectroscopy reveals the simultaneous existence of three low-spin systems in each case that are attributed to various protonation and/or conformational stages in the heme pocket. Electron nuclear double resonance (ENDOR) spectroscopy demonstrates that the thiol sulfurs are, at least in part, protonated. Overall, the results not only demonstrate the good accessibility of the NP4 heme center by biologically relevant thiols, but also represent the first structural characterization of a ferriheme protein in complex with L-cysteine L-homocysteine.