ANALYSES OF CDNA AND RECOMBINANT PROTEIN FOR A POTENT VASOACTIVE PROTEIN IN SALIVA OF A BLOOD-FEEDING BLACK FLY, SIMULIUM-VITTATUM

A cDNA was cloned from the salivary glands of a blood-feeding black fl y Simulium vittatum. The encoded protein has been given the name Simul ium vittatum erythema protein or SVEP, because of its ability to incre ase blood perfusion in skin capillaries, resulting in the well-charact erized erythema of black fly bites. The full-length cDNA contains 548 base pairs which encode 152 amino acid residues of the nascent protein . Post-translational processing produces a mature, secreted protein of 133 residues with a molecular mass of 15.4 kDa. Recombinant SVEP (rSV EP) was produced in a baculovirus expression system and purified by a one-step reversed-phase HPLC procedure. Analyses of physical propertie s and biological potency demonstrated fidelity of rSVEP to the native protein. Recombinant SVEP relaxed rabbit aorta preparations when preco nstricted with 2 mu mol l(-1) phenylephrine or 25 mmol l(-1) K+ but no t with 60 mmol l(-1) K+. Further, the rSVEP-induced relaxation respons e of phenylephrine-constricted aorta was inhibited by glibenclamide (1 0 mu mol l(-1)), suggesting that at least part of its action to relax smooth muscle may result from the opening of ATP-dependent K(+)channel s. SVEP is a novel salivary-gland-derived vasoactive protein that may be essential for blood feeding by black flies and could potentially en hance transmissionof filarial parasites.