Interaction of the glycoprotein excreted by Pseudoalteromonas antarctica NF 3 with phosphatidylcholine liposomes

Abstract

The ability of an exopolymer of glycoproteic character (GP) excreted by a new gram-negative specie, Pseudoalteromonas antarctica NF 3, to coat phosphatidylcholine (PC) unilamellar liposomes and to protect these bilayer structures against the solubilizing action of the non-ionic surfactant Triton X-100 (T X-100) has been investigated. TEM micrographs of freeze fractured liposome/GP aggregates reveal that the presence of GP in liposome suspensions resulted in the formation of a continuous thin film that coated tightly these bilayer structures. The complete coating of these vesicles was already achieved at a PC:GP weight ratio of about 9:1. Higher GP amounts (up to a PC:GP weight ratio of 1:1) led to a progressive growth of this film which exhibited at the highest GP proportion a multilayered structure. An increasing resistance of PC liposomes to be solubilized by T X-100 took place as the proportion of GP in the system rose, although this protective effect was more effective at low GP proportions (PC:GP weight ratios from 9:1 to 4:1). Thus, although in the range of PC:GP weight ratios from 9:1 to 6:4 a direct dependence was found between the growing of the covering structure and the resistance of the coated liposomes to be solubilized by T X-100, the best protection effect occurred when this covering structure was a thin and continuous film with a thickness not higher than 15–20 nm (PC:GP weight ratios ranging from 9:1 to 4:1).