The work in this thesis can be divided into two sections, namely the study of delicious peptide, a food flavour and the antimicrobial peptide lactofenicin B. The main interest in these compounds is in terms of structure and conformation adopted in solution and how this relates to their mode of action. Delicious peptide was studied initially by 1H NMR spectroscopy for evidence of a specific solution structure. Results show that delicious peptide does not adopt a regular conformation in solution. Molecular dynamics simulations of this peptide show the flexibility of the peptide structure in solution. Quenched molecular dynamics simulations were used to search for low energy conformers of the peptide. The results suggest that the flavour of the peptide is produced by interaction of basic and acidic regions in the peptide. The work was extended to examine delicious peptide analogues with similar flavour characteristics. The results obtained suggest that similar interactions of basic and acidic regions occur for these peptides to produce a savoury flavour. The antimicrobial peptide Lactofemcin B was synthesised by Fmoc poly-amide synthesis. Problems with the synthesis occurred due to the protecting groups used for the five arginine residues present in the sequence. Predictive modelling studies on Lactofenicin B peptide, derived from bovine lactofenicin protein suggest that the peptide adopts a region of alpha-helical conformation in solution. The flexibility of the peptide was studied by molecular dynamics in solution and simulations of other environmental conditions were carried out by variation of electrostatic interactions using dielectric constants for membrane, TFE and water environments. The results suggest the beta-helical conformation is most stable in an environment such as trifluoroethanol, the peptide showing more flexibility in aqueous solution. Experimental results for the peptide confirm the flexibility of the peptide in solution. CD results show that lactofenicin B has no specific conformation in solution, although an beta-helical conformation is adopted in trifluoroethanol. The peptide also adopts a beta-sheet conformation in low concentrations of SDS micelle and therefore its conformation is dependant on environmental conditions. NMR studies show that the peptide, although flexible in solution, shows short-range NOE interactions that suggest a local beta-helical conformation may be present. However the overall conformation for the peptide is a flexible one.

Cervical cancer is the second most common cancer among women worldwide and human papillomavirus (HPV) is a prerequisit for the development of this cancer. HPV belongs to the Papillomaviridae family and infects the basal layer of epithelial cells where it generally progresses into warts or condylomas. HPV can only reproduce in differentiating epithelia and it is therefore difficult to study the natural infection of HPV. More than 100 HPV types exist and they are divided into different genera based on their L1 open reading frame sequence. Most of the HPV types in the alpha-papillomavirus genus infect the mucosal epithelium while HPVs from the beta-papillomavirus genus usually infect cutaneous epithelial cells. Presently, it is not known what decides the anatomical tropism and our aim was to study determinants of this tropism. By using HPV virus like particles (VLP) and pseudovirus we found that VLPs from the two alpha-papillomaviruses HPV-6 and HPV-16 interacted with cell-surface heparan sulfate (HS) for initial attachment. When we labelled HPV VLPs with a fluorescent dye to study internalization HPV-6 was more strongly inhibited than HPV-16. Furthermore, a pseudovirus infection assay demonstrated that the beta-papillomavirus HPV-5 was less dependent on HS for infection than HPV-16. By analyzing the isoelectric point (p1) of the HPV L1 capsid protein we found that alpha HPV types were more positively charged than beta HPV types. Also, HPV-6 had a higher positive charge than HPV-16. Thus, the inhibition of the negatively charged heparin against HPV infection was clearly related to the charge of the HPV L1 capsid. This suggested that the initial interaction could be one of the determinants of tropism although not the sole factor. Lactoferrin is a protein found in milk, saliva, semen, tear fluid and endocervical secretions that has antiviral activities. Both human and bovine lactoferrin inhibited HPV infection but we found no significant differences in inhibition of alpha- and beta-papillomavirus infection. We could however demonstrate that different lactoferricins, small peptide derivates from the N-terminal part of lactoferrin, were able to inhibit HPV infection. This antiviral activity depended on lactoferricin peptide, HPV type and cell origin. The regulation of HPV gene expression in the host cell could also determine HPV tropism. The HPV long control region (LCR) contains cis-responsive elements that regulate HPV transcription and the epithelial tropism of HPV is determined by epithelial specific constitutive enhancers in the LCR. It has been hypothesized that the combination of transcription factors in the host cell determines the cell-type-specific expression. In cells with a skin origin the HPV-5 LCR was twice as efficient in transcriptional activation compared to HPV-16 LCR, while in cervical cells the HPV-16 LCR was almost twice as effective in activating transcription compared to HPV-5 LCR. To conclude, alpha- and beta-papillomaviruses differed regarding their ability to infect cells and regulate viral gene expression. These abilities corresponded with their natural host cells and suggested that HPV anatomical tropism could be determined at several steps in the HPV life cycle.