Mode of Interaction of Amphiphilic α-Helical Peptide with Phosphatidylcholines at the Air−Water Interface

• Published in: Langmuir 2006-01, Vol.22 (3), p.1182-1192
• Main Authors: Nakahara, Hiromichi, Nakamura, Shohei, Hiranita, Takato, Kawasaki, Hideya, Lee, Sannamu, Sugihara, Gohsuke, Shibata, Osamu
• Format: Article
• Language: English
• Subjects: Adsorption; Air; Amino Acid Sequence; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Microscopy, Atomic Force; Microscopy, Fluorescence; Molecular Sequence Data; Peptides - chemistry; Phosphatidylcholines - chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Surface physical chemistry; Water - chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la0524925

Surface pressure (π)−, surface potential (ΔV)−, and dipole moment (μ⊥)−area (A) isotherms and morphological behavior were examined for monolayers of a newly designed 18-mer amphiphilic α-helical peptide (Hel 13-5), DPPC, and DPPC/egg-PC (1:1) and their combinations by the Wilhelmy method, ionizing electrode method, fluorescence microscopy (FM), and atomic force microscopy (AFM). The newly designed Hel 13-5 showed rapid adsorption into the air−liquid interface to form interfacial films such as a SP-B function. Regardless of the composition and constituents in their multicomponent system of DPPC/egg-PC, the collapse pressure (πc; ∼42 mN m-1) was constant, implying that Hel 13-5 with the fluid composition of egg-PC is squeezed out of Hel 13-5/DPPC/egg-PC monolayers accompanying a two- to three-dimensional phase transformation. FM showed that adding a small amount of Hel 13-5 to DPPC induced a dispersed pattern of ordered domains with a “moth-eaten” appearnce, whereas shrinkage of ordered domains in size occurred for the DPPC/egg-PC mixture with Hel 13-5. Furthermore, AFM indicated that (i) the intermediate phase was formed in pure Hel 13-5 systems between monolayer states and excluded nanoparticles, (ii) protrusions necessarily located on DPPC monolayers, and (iii) beyond the collapse pressure of Hel 13-5, Hel 13-5 was squeezed out of the system into the aqueous subphase. Furthermore, hysteresis curves of these systems nicely resemble those of the DPPC/SP-B and DPPC/SP-C mixtures reported before.