Behavior of insect defensin A at the air/water interface

• Published in: Colloids and surfaces, B, Biointerfaces B, Biointerfaces, 1996-09, Vol.7 (3), p.135-143
• Main Authors: Maget-Dana, Régine, Ptak, Marius
• Format: Article
• Language: English
• Subjects: Air/water interface; Antibacterial protein; Insect defensin A; Protein adsorption; Surface properties
• ISSN: 0927-7765; 1873-4367
• DOI: 10.1016/0927-7765(96)01292-1

The surface behavior of insect defensin A, an inducible antibacterial protein isolated from the larvae of the fleshfly Phormia terranovae, has been investigated. Defensin A is able to adsorb at the air/water interface from an aqueous solution. The adsorption kinetics show two regions corresponding to adsorption and interfacial rearrangements. Both the maximum pressure reached in the course of adsorption and the equilibrium spreading pressure, π e, rank defensin A among surface-active proteins. The data extracted from the pressure-area (π-A) isotherms suggest that the defensin A molecule is partly unfolded at the air/water interface and may self-associate under compression. The stability of the defensin monolayer is greatest at basic pH (around the isoelectric point) and increases with increase in the ionic strength of the subphase. The presence of 2 mM Ca 2+ ions, pH 7.2, gives rise to an increase in the monolayer compressibility. Compression-expansion cycles present a wide hysteresis interpreted as the result of simultaneous desorption, self-association and folding of the defensin molecules in the course of the compression process.