Effect of Tryptophan Residues on Adsorption of a Cationic Arginine Rich Polypeptide by Hydroxyapatite Nanoparticles and Following Translocation of the Polypeptide Through a Lipid Vesicle Membrane

Abstract

Hydroxyapatite (abbreviated to HAp), in general, adsorbs a polypeptide, resulting in a HAp-peptide complex. In the present paper the Hap was of a nanosized particle and peptide was poly-L-arginine (abbreviated to poly(Arg)) or copoly(L-arginine/ L-tryptophan = 4:1) (abbreviated to poly(Arg,Trp)). Physicochemical properties of these complexes were quite different with each other due mainly to the presence or absence of tryptophan residues on the polymer chain. The adsorption amount of poly(Arg,Trp) on HAp was much larger than that of poly(Arg). Zeta potential of the HAp-poly(Arg,Trp) complex was far lower than that of the HAp-poly(Arg) complex. Considering these facts, it was concluded that hydrophobic interaction between Trp residues of poly(Arg,Trp) induced an adsorption bilayer on HAp, while poly(Arg) simply formed an adsorption monolayer through electrostatic interaction. On the other hand, structural flexibility of a copolymer and its translocation through a lipid membrane were lower and slower in poly(Arg,Trp) than in poly(Arg).