The mechanism of histatin 5 induced cell death in Saccharomyces cerevisiae
Zakhari, Joseph S.
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Histatin 5 is a potent antifungal peptide endogenously produced by the parotid, sublingual and submandibular glands in humans. The potent antifungal properties afforded provide histatin 5 as an enticing biological therapeutic in treating oral candidiasis as well as other opportunistic yeast infections in immunocompromised individuals. As Candida albicans gains resistance to the current pharmacotherapies, it is pertinent to elucidate novel approaches in treating this pathogen. While a plethora of research has been performed studying histatin 5, its mechanism of action within C. albicans and other yeast species remains unresolved. Herein, we report on histatin 5 and suggest a mechanism of killing within a Saccharomyces cerevisiae model. Using haploid genetic knockouts, several genes of interested were tested in viable culture at the 50% lethal dose of histatin 5. Cells were further analyzed as being resistant or hypersensitive to histatin 5. Genes of interest and protein gene products were categorized in six distinct categories including cell surface transport, ion channels and osmoregulation, ionic/osmotic stress response, calcineurin regulation, oxidative stress response and finally cell wall and plasma membrane integrity. Histatin 5 internalizes via interactions with Ssa1, an Hsp70 family member, via initial binding then subsequent transfer to polyamine transporters Dur3 and Ptk2. Once inside the cell, histatin 5 operates through at least two pathways. Histatin 5 causes a deregulation of ionic gradients and membrane potential through cell surface ion channels Pma1 and Trk1. Initial osmotic stress activates regulatory pathways including high osmolarity glycerol (Hog1) pathways as well as the calcium dependent phosphatase calcineurin. While the osmotic stress is the immediate response to histatin 5 internalization, it is believed that histatin 5 also travels to the actively respiring mitochondria via interactions with cytosolic Ssa1. Histatin 5 enters the mitochondria and disrupts the electron transport chain ultimately producing highly reactive free radicals and reactive oxygen species. These species consequently damage DNA, lipids and proteins and are the main factors involved cell death. While further research is necessary, the establishment of necessary gene products for histatin 5 induced killing in S. cerevisiae grants mechanistic clarity, hopefully allowing for the development and advancement of histatin 5 mediated therapies in the future.
Thesis (M.A.)--Boston University