This proposal comprises two subproposals that use similar methods. 1. Mammalian dipeptidyl peptidase IV(DPP IV) is a highly glycosylated serine protease, that releases N-terminal dipeptides from oligopeptides. Itis both an integral membrane protein (CD26) and a plasma protein, the physiological role of which isunknown (Hosono et at., 1999). Among its diverse physiological roles, DPP IV removes X-Pro, His-Ala ortyr-Ala dipeptides from the N-termini of hormones such as neuropeptide Y and substance P. It wasdiscovered in snake venoms by Jorge da Silva and Aird (2000). DPP IVs role in venom may be to preventa hypertensive response on the part of the envenomated prey by inactivating vasoconstrictive peptidylhormones (Aird, 2002). It may also contribute to the persistent hypotension seen in human envenomationand to inflammation. The present study should shed light on the role of human soluble DPP IV.2. Snake venom enzymes that cleave phosphate esters were first discovered when venomphosphodiesterase (PDE) was reported by Gulland and Jackson (1938). Despite this long history, PDE'srole in envenomation remained enigmatic until Aird (2002) proposed that its function might be to releaseendogenous purines, which would immobilize the prey via hypotension and suppression ofneurotransmitter release. Snake venom PDE has attracted great interest because of its utility in nucleicacid studies (>2,400 Medline citations). Despite its near reagent status, its structure is unknown. Mostforms of PDE are membrane-bound or cytosolic, whereas venom PDE is extremely soluble, so as tofunction in the extracellular fluid of prey organisms. It has broad substrate specificity [Razzell and Khorana,1959; Laskowski, 1980], making it well suited to the rapid liberation of adenosine nucleotides from variousoligonucleotide precursors, a central theme in envenomation (Aird, 2002). It also has pyrophosphataseactivity [Laskowski, 1980], releasing nucleotides and pyrophosphate from nucleoside triphosphates.Nucleotides are rapidly degraded to nucleosides by 5'-nuc!eotidase, present in both venom and preytissues. Venom PDE was the first enzyme reported to have an active site threonine forming a covalent(phosphorylated) intermediate [Burgers et al., 1979; Gulp and Butler, 1986]. These functionalcharacteristics suggest that it is likely to be structurally unique.
Showing the most recent 10 out of 20 publications
