Structural Determination of Antimicrobial Peptides Derived from Human Lactoferricin and Ovalbumin

This dissertation, "Structural Determination of Antimicrobial Peptides Derived From Human Lactoferricin and Ovalbumin" by Ching-mang, Queenie, Wong, 王靜萌, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled STRUCTURAL DETERMINATION OF ANTIMICROBIAL PEPTIDES DERIVED FROM HUMAN LACTOFERRICIN AND OVALBUMIN Submitted by Wong Ching Mang Queenie for the degree of Master of Philosophy at The University of Hong Kong in August 2006 The three-dimensional structures of two antimicrobial peptides, LfcinH from 18-42 the human milk protein lactoferrin (LfH) and OVA from the egg white 277-291 protein ovalbumin (OVA), were determined using circular dichroism (CD) and two-dimensional nuclear magnetic resonance (NMR) spectroscopic techniques. Distinct from its homologous peptide (LfcinB ) from the bovine lactoferrin 1-25 (LfB), which adopts a distorted antiparallel β-sheet conformation, LfcinH is 18-42 partly structured with around 20% helical content in aqueous solution. The segment from Cys3 to Arg14 was found to be well defined with a short helix extending from Arg8 to Arg11. The helical characteristic of the peptide closely resembles its corresponding conformation in the intact LfH, as well as in full length LfcinH . Following the short helix, a type IV turn between Lys12 and 1-47 Gly15 allows the fragment from Pro17 to Cys20 folds back in an antiparallel alignment with Cys3 to Arg12. The disulfide linkage between Cys3 and Cys20 provides the anchor for closure of the loop to assume an amphiphilic structure, which is typical of the membrane disruptive helical antimicrobial peptides. Based on the solution structure, potential mechanisms for the antimicrobial action of LfcinH can be proposed. The distinct conformations of 18-42 LfcinH and its homologous peptide (LfcinB ) suggest a difference in their 18-42 1-25 mode of actions. In contrast to LfcinH, OVA is unordered in aqueous solution. 18-42 277-291 However, upon association with membrane mimicking sodium dodecyl sulfate (SDS) micelles, it folds into a well-defined extended structure with a type I turn through Leu7 to Met10. Instead of being amphiphilic, micelle-bound OVA undergoes side chain rearrangements that result in clustering of 277-291 hydrophobic residues which are flanked by two dispersed and charged regions at both termini of the peptide. Closely resembling the extended family of cationic peptides, OVA lacks of a canonical amphiphilic secondary conformation. 277-291 Due to this structural resemblance, it is logical to speculate that their mode of action is similar. This study has elucidated the three-dimensional structures of two antimicrobial peptides, LfcinH and OVA . Such knowledge should aid in 18-42 277-291 understanding the molecular modes of action of antimicrobial peptides as well as their broad spectrum of activities. DOI: 10.5353/th_b3693473 Subjects: Lactoferrins Serpins Peptide antibiotics