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J Biol Chem. 2014 Aug 8;289(32):22172-82. doi: 10.1074/jbc.M114.570143. Epub 2014 Jun 18.

A cleavage-potentiated fragment of tear lacritin is bactericidal.

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From the Department of Integrated Science and Technology, James Madison University, Harrisonburg, Virginia 22807.
the Warfighter Refractive Eye Surgery Program and Research Center at Fort Belvoir, Fort Belvoir, Virginia 22060, and.
the Departments of Public Health Sciences, Systems and Information Engineering.
Cell Biology, Ophthalmology, and Biomedical Engineering, University of Virginia, Charlottesville, Virginia 22908


Antimicrobial peptides are important as the first line of innate defense, through their tendency to disrupt bacterial membranes or intracellular pathways and potentially as the next generation of antibiotics. How they protect wet epithelia is not entirely clear, with most individually inactive under physiological conditions and many preferentially targeting Gram-positive bacteria. Tears covering the surface of the eye are bactericidal for Gram-positive and -negative bacteria. Here we narrow much of the bactericidal activity to a latent C-terminal fragment in the prosecretory mitogen lacritin and report that the mechanism combines membrane permeabilization with rapid metabolic changes, including reduced levels of dephosphocoenzyme A, spermidine, putrescine, and phosphatidylethanolamines and elevated alanine, leucine, phenylalanine, tryptophan, proline, glycine, lysine, serine, glutamate, cadaverine, and pyrophosphate. Thus, death by metabolic stress parallels cellular attempts to survive. Cleavage-dependent appearance of the C-terminal cationic amphipathic α-helix is inducible within hours by Staphylococcus epidermidis and slowly by another mechanism, in a chymotrypsin- or leupeptin protease-inhibitable manner. Although bactericidal at low micromolar levels, within a biphasic 1-10 nM dose optimum, the same domain is mitogenic and cytoprotective for epithelia via a syndecan-1 targeting mechanism dependent on heparanase. Thus, the C terminus of lacritin is multifunctional by dose and proteolytic processing and appears to play a key role in the innate protection of the eye, with wider potential benefit elsewhere as lacritin flows from exocrine secretory cells.


Bacterial Metabolism; Cornea; Eye; Innate Immunity; Lacritin; Phosphatidylethanolamine; Protein Targeting; Serine Protease; Tears

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