Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Chemistry

Supervisor

Ken Yeung

Abstract

Current drug therapies have lost their effectiveness in controlling the fungal species known as C. albicans; therefore, the need for newer drugs becomes crucial. Histatin 5 (Hst 5), a naturally occurring peptide found in the oral cavity, has demonstrated strong effects on controlling candidiasis. Here, we have proposed that the adhesion of cells through surface proteins is an important process. To allow the analysis of surface proteins, the concept of on-whole cell tryptic digestions were developed. This on-target approach allows for isolation of the peptides of interest, while greatly reducing digestion times.

To study the effects of Histatin 5 on surface proteins, live cells were adhered to slides pre-coated with human serum albumin (HSA); and subsequently, treatments with Hst 5 were done. Mass spectrometry was used to correlate changes in ion counts to protein expressions. Preliminary work done by MALDI MS verified that changes in ion counts occurred, as well as tentative protein identifications. Then, HPLC-ES-MS/MS was used to verify proteins and their biological processes. Few proteins were seen from the cell surface, but, their presence indicated the success of our on-target approach. Three other processes were found; virulence, mitochondrial associated and nucleic acid binding. Hst 5 was shown to decrease the expression of proteins involved in the virulence, supporting Hst 5 as an antifungal agent. The identified proteins involved in the last two pathways have provided additional support for the speculation that cellular respiration in the mitochondria may be the true target of Hst 5.


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