Preparation of a novel aggregate like sugar-ball micelle composed of poly(methylglutamate) and poly(ethyleneglycol) modified by lactose and its molecular recognition by lectin.

We report the preparation and characteristics of a novel micellar aggregate of an amphiphilic diblock copolymer, poly(methylglutamate) (PMG)-poly(ethyleneglycol) (PEG), whose terminus was modified by lactose lactone (LA). Due to the terminal LA moiety, this aggregate could be specifically recognized by RCA120 lectin. PMG-PEG-LA was synthesized by polymerizing the N-carboxy anhydride of L-glutamic acid gamma-methyl ester with H2N-PEG-LA as a polymerization initiator. By applying a fluorescence method using pyrene as a probe molecule, we found that PMG-PEG-LA could form the aggregate in aqueous solution. Fluorescence measurements showed that the critical aggregation concentration (C.A.C.) was 1.1 x 10(-5) M. The average diameter of the aggregate was 220 nm at 25 degrees C, as determined by the dynamic light scattering method. Circular dichroism measurements for the aggregate solution showed that the PMG residue took an alpha-helical structure, and that they associated to constitute the hydrophobic core of the aggregate. By adding RCA120 lectin to the aggregate solution, the turbidity of the solution increased rapidly, due to association of the aggregates. This implies that the aggregate could be recognized by lectin, and also suggests that sugar residues locate at the surface of the aggregates. From these findings, we concluded that the PMG-PEG-LA molecules form an aggregate like a "sugar ball" micelle, whose surface is covered by the sugar moieties. Application of the present aggregate system as a drug carrier is briefly discussed.