Mechanism of the leakage induced on lipid model membranes by Rz1 lipoprotein, the bacteriophage lambda Rz1 gene product: A fluorescence study

The leakage of aqueous contents of neutral (dipalmitoylphosphatidylcholine/ cholesterol) liposomes as induced by Rz1, a proline-rich lipoprotein, the b acteriophage lambda Rz1 gene product, was studied. Fluorescence enhancement assay with Tb3+/dipicolinic acid and self-quenching assays with carboxyflu orescein and fluorescein isothiocyanaten-dextran were used to monitor the R z1-induced leakage from neutral liposomes. The results demonstrated that Rz 1 caused local membrane destabilization leading to the leakage of the Lipos ome contents. The extent of the leakage was independent of the molecular ma ss of the liposome-entrapped solutes in the range of 376-4000 Da. The kinet ics of Rz1-liposome leakage was very similar to that obtained with detergen t Triton X-100 for all the solutes used. The results suggested that Rz1 can act as a detergent; i.e., by interacting with lipids on both sides of the liposome membranes (inducing perturbation in the lipid packing within the b ilayer), it facilitates the transfer of encapsulated molecules into the ext ernal liposome environment. The importance of this result for Rz1 physiolog ical function is discussed.