Necator americanus (human hookworm) aspartyl proteinases and digestion of skin macromolecules during skin penetration

The infective larvae of Necator americanus were shown to secrete all mechan istic classes of proteolytic enzymes with two overall pH optima of 6.5 and 8.5 using fluorescein isothiocyanate-labeled casein as the substrate. Since infective larvae are obligate skin penetrators, the effect of each of thes e enzyme classes against macromolecules derived from human skin was examine d. Larval secretions were shown to degrade collagen types I, III, IV, and V , fibronectin, laminin, and elastin. All the skin macromolecules tested wer e hydrolyzed by aspartyl proteinase activity, which was inhibitable by peps tatin A. Collagen and elastin was also hydrolyzed by metalloproteinase acti vity, while the serine proteinase activity hydrolyzed only elastin. As a co nsequence of these experiments, the effect of proteinase inhibitors on the penetration of live larvae through hamster skin was tested. Larval penetrat ion was significantly inhibited only by pepstatin A, confirming the importa nce of the aspartyl proteinase activity during the skin penetration process .