1ntf
From Proteopedia
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Crystal Structure of Cimex Nitrophorin
Overview
Certain bloodsucking insects deliver nitric oxide (NO) while feeding, to, induce vasodilation and inhibit blood coagulation. We have expressed, characterized, and determined the crystal structure of the Cimex, lectularius (bedbug) nitrophorin, the protein responsible for NO storage, and delivery, to understand how the insect successfully handles this, reactive molecule. Surprisingly, NO binds not only to the ferric, nitrophorin heme, but it can also be stored as an S-nitroso (SNO), conjugate of the proximal heme cysteine (Cys-60) when present at higher, concentrations. EPR- and UV-visible spectroscopies, and a crystallographic, structure determination to 1.75-A resolution, reveal SNO formation to, proceed with reduction of the heme iron, yielding an Fe-NO complex., Stopped-flow kinetic measurements indicate that an ordered reaction, mechanism takes place: initial NO binding occurs at the ferric heme and is, followed by heme reduction, Cys-60 release from the heme iron, and SNO, formation. Release of NO occurs through a reversal of these steps. These, data provide, to our knowledge, the first view of reversible, metal-assisted SNO formation in a protein and suggest a mechanism for its, role in NO release from ferrous heme. This mechanism and Cimex nitrophorin, structure are completely unlike those of the nitrophorins from Rhodnius, prolixus, where NO protection is provided by a large conformational change, that buries the heme nitrosyl complex, highlighting the remarkable, evolution of proteins that assist insects in bloodfeeding.
About this Structure
1NTF is a Single protein structure of sequence from Cimex lectularius with HEM as ligand. Full crystallographic information is available from OCA.
Reference
Heme-assisted S-nitrosation of a proximal thiolate in a nitric oxide transport protein., Weichsel A, Maes EM, Andersen JF, Valenzuela JG, Shokhireva TKh, Walker FA, Montfort WR, Proc Natl Acad Sci U S A. 2005 Jan 18;102(3):594-9. Epub 2005 Jan 6. PMID:15637157
Page seeded by OCA on Sat Nov 24 23:47:01 2007
