Date of Graduation

8-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Cell & Molecular Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor

David S. McNabb

Committee Member

Roger E. Koeppe II

Second Committee Member

Gisela F. Erf

Third Committee Member

Ralph L. Henry

Fourth Committee Member

Suresh K. Thallapuranam

Abstract

Candida species are the fourth leading cause of nosocomial infection. The increased incidence of drug-resistant Candida species has emphasized the need for new antifungal drugs. Histatin 5 is a naturally occurring human salivary antifungal peptide and the first line of defense against infections of the oral cavity. This research has focused on understanding the activity of histatin 5, and subsequently designing novel peptides that may serve as models for the further development of therapeutics to treat fungal infection.

This objective has been achieved in three steps: studying the structural requirement of histatin 5 involved in antifungal activity, the identification of a short peptide sequence, referred to as KM motif, important for fungicidal activity, and finally, the development of a novel antifungal peptide with potent activity.

In the initial phase of this work it was demonstrated that reversing the sequence of histatin 5 C-16 peptide to create a retro peptide did not interfere with the fungicidal activity or secondary structure of the peptide. This suggested that the spatial arrangement of amino acid residues was more relevant for fungicidal activity than the actual peptide sequence.

In the second phase of the work, we identified and characterized a five amino acid sequence, termed the KM motif, within histatin 5 that maintained fungicidal properties. Although this short peptide was less active than histatin 5, the data suggested it was killing fungi via a mechanism similar to histatin 5.

In the final phase, a novel antimicrobial peptide, termed KM-12, was generated containing two KM motifs dimerized via disulfide bonds. The activity of KM-12 on C. albicans was approximately fifteen times more

potent than the monomeric peptide and ten times more active than the native histatin 5. KM-12 was shown to have antifungal activity with several Candida species, including fluconazole resistant species. In conclusion, KM-12 is promising antifungal peptide that will serve as a lead candidate for the development of antifungals peptide for pharmaceutical applications.

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