Abstract
Although the mesquite plant (Prosopis velutina) is not as widely distributed as some other allergenic species, its pollen can induce serious pollinosis in areas where it is localized. We previously isolated and characterized a peptidase from mesquite pollen with trypsin-like specificity (peptidase Imes) (Matheson, N., Schmidt, J., and Travis, J. (1995) Am. J. Respir. Cell Mol. Biol. 12, 441-448). Now we have characterized a second enzyme with specificity for hydrophobic residues (mesquite pollen peptidase IImes). This enzyme has a molecular mass near 92 kDa and activity that was not affected by reducing or chelating agents but was inhibited by specific synthetic serine proteinase inhibitors and the aminopeptidase inhibitor bestatin. However, it was not inhibited by human plasma proteinase inhibitors, nor did it inactivate any of those tested. The enzyme possessed amidolytic activity against p-nitroanilide substrates most effectively after alanine residues and also displayed aminopeptidase activity against non-p-nitroanilide peptides with a preference for phenylalanine. This specificity for hydrophobic amino acid residues was corroborated by inhibition studies with chloromethyl ketone and organophosphonate inhibitors. More interesting from a physiological point of view is that the bioactive peptides, angiotensins I and II and vasoactive intestinal peptide, were also hydrolyzed rapidly, indicating an ability of peptidase IImes to act also as an oligopeptidase. Because these bioactive peptides play a role in the inflammatory responses in allergic asthma, our data suggest that the purified mesquite pollen peptidase IImes may be involved in the degradation of neuro- and vasoactive peptides during pollen-initiated allergic reactions.
Highlights
Asthma is an allergic inflammation of the lungs which can occur after allergen sensitization
Epithelial cells lining the airways are shed during this inflammatory response, removing a protective barrier [2] and are a source of neutral endopeptidase (which normally degrades various bronchoconstrictor peptides [7]) while exposing nerve endings [8] that secrete neuropeptides such as vasoactive intestinal peptide (VIP)1 and substance P, and vasoactive peptides
Other proteins are released, of which several have proven to be oligopeptidases (14 –16). Because these latter enzymes appear to be members of a family of pollen oligopeptidases with varying specificities for peptide hydrolysis, we propose to name them, at least temporarily, as: peptidases Imes and Irag, peptidase IIrag, and, as described in this report, peptidase IImes, an enzyme that rapidly degrades VIP, angiotensin II, and its precursor, angiotensin I
Summary
Asthma is an allergic inflammation of the lungs which can occur after allergen sensitization Such inflammatory responses are normally meant to defend against invading organisms or particulates or to effect tissue repair and are beneficial; in asthma, the response becomes exaggerated (perhaps because of a hereditary predisposition [1]), leading to adverse effects on the airways [2]. Macrophages phagocytize the allergens introduced to the lungs by exposure to various environmental irritants such as dust, pollutants, and pollen, and process them to smaller fragments As antigenpresenting cells, they activate T-cells [3, 4] to stimulate B-cells to produce IgE. Pollen is one of the major initiators of allergic asthma This gamete contains proteins (allergens) that are solubilized in the airway mucus and proceed to induce an immunological response. We suggest that through exo- and oligopeptidase activity, pollen may have the capability for participation in the inflammatory processes in allergic asthma by mechanisms other than those involving its immunological component
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