INBRE Seminar Series
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Dr. F. Ann WalkerNovel NO-Releasing Heme Proteins |
The components of the saliva of blood-sucking insects that aid in the insects' ability to obtain a sufficient blood meal include a wide variety of molecules that are 1) prostaglandins that cause skin vasodilation, or 2) peptides or other components that inhibit various enzymes of the clotting cascade, or 3) components that prevent platelet aggregation, or 4) components that cause vasodilation, and/or 5) components that prevent secreted histamine from initiating the immune response. We have discovered some unique NO-bound heme proteins, called nitrophorins, which release NO and bind histamine, thus aiding by means of scenarios 3, 4 and 5, and one of them also has anti-clotting activity against factor Xa of the clotting cascade (scenario 2). The nitrophorins (NP) from the salivary glands of the kissing bug (Rhodnius prolixus) have been cloned, sequenced, expressed, purified and characterized by optical, EPR, NMR, FTIR and resonance Raman spectroscopies, X-ray crystallography, and electrochemistry. These are unique heme proteins that are stabilized in the Fe(III) oxidation state, thus insuring that NO can dissociate from the proteins upon the insect's injection of them into the tissues of the victim, thus diluting the NO-binding proteins by approximately 100-fold. There are four nitrophorins in the R. prolixus saliva that display interesting similarities and differences. All have molecular weights of about 20 kD. In contrast, the bedbug (Cimex lectularius) has one nitrophorin with a molecular weight of about 30 kD and no sequence or structural homology with the Rhodnius proteins, and even a different heme proximal ligand. Hence, it appears that these two insects from different families of Hemiptera developed the ability to stabilize NO for long periods of time by binding it to a heme protein via convergent evolution. Current work to be discussed involves preparation and investigation of the electrochemistry of site-directed mutants of the R. prolixus nitrophorins and detailed NMR investigations aimed at studying the heme binding site. |
| Dr. F. Ann Walker is Regents Professor of Chemistry and Professor of Biochemistry and Molecular Biophysics at the University of Arizona. She received her Ph.D. in 1966 from Brown University, and in 2006 received the Alfred Bader Award in Bioinorganic Chemistry from the American Chemical Society. She has authored nearly 150 papers. |