Study of a Model α-Helix Peptide’s Surface Properties by Langmuir Monolayer Techniques and Surface FTIR

Abstract

Cell membranes have been shown to be able to change the conformation of proteins/peptides. However, the structure of the cell membrane is complicated and has been divided to three regions: the hydrophobic region containing alkyl chains, the hydrophilic head group, and the hydration layer, or lipid-water interface, which exists between the hydrophilic head group and the bulk water solution, but with lower dielectric constant compared with fully hydrated water. The air-water interface has been used to mimic the structure of the hydration layer because of their similar dielectric constant.1,2 Some proteins were found to form a stable Langmuir monolayer and accumulate at the air-water interface. For example, α-synclein, a membrane protein containing 140 amino acids, is unstructured in aqueous solution but changes its conformation to α-helix at the air-water interface. This incites interest to investigate short motifs of α-helix to form a stable Langmuir monolayer at the air-water interface. In this thesis, a peptide with sequence of YAAAA(KAAAA)4 (referred as Pep25 hereafter) was used as a model peptide of α-helix to spread at the air-water interface, because our group has determined the conformation of Pep25 in residue level by the 13C isotope-edited FTIR. Langmuir monolayer technique together with IRRAS showed that Pep25 does not form a typical Langmuir monolayer at the interface. Potential plans to make Pep25 to form a stable monolayer are also discussed in this thesis.