A comparative study of band 3 aggregation in erythrocyte membranes by melittin and other cationic agents

The technique of laser flash-induced transient dichroism has been used to measure the rotational diffusion of eosin-labelled band 3 proteins in erythrocyte ghosts. A retardation in the mobility of band 3, measured subsequent to the addition of a variety of polyvalent cationic species, has been interpreted to reflect aggregation or 'clustering' of the protein in the plane of the membrane. A comparative study is reported between three such aggregators: melittin, polylysine and Zn2+, wherein their respective abilities to induce aggregation have been measured under varying conditions. Unlike that for melittin, band 3 aggregation by polylysine and Zn2+ is shown to be sensitive to proteolytic degradation of the membrane and to the ionic strength of the surrounding medium. Studies with fragments of melittin derived from its chymotryptic cleavage show the hydrophilic C-terminal 20-26 section to possess independent aggregating ability, but also the requirement of the 1-19 hydrophobic section to be attached in order to prevent reversibility by high ionic strength buffers. Melittin is also shown to have a unique ability to aggregate bacteriorhodopsin reconstituted into DMPC vesicles, which is partially retained by its 1-19 but not by its 20-26 fragment.