title: Novel polysaccharide-protein-based amphipathic formulations.
abstract: Previous results showed that the cell-surface esterase from Acinetobacter venetianus RAG-1 enhances the emulsification properties of the polymeric bioemulsifier emulsan and its deproteinated derivative apoemulsan (Bach H, Berdichevsky Y, Gutnick D (2003) An exocellular protein from the oil-degrading microbe Acinetobacter venetianus RAG-1 enhances the emulsifying activity of the polymeric bioemulsifier emulsan. Appl Environ Microbiol 69:2608-2615). Here we show that in the presence of the his-tagged recombinant esterase from RAG-1, 18 different polysaccharides from microbial, plant, insect and synthetic sources formed hexadecane-in-water emulsions. Emulsifying activities were distributed over a 13-fold range from over 4800 U/mg protein/mg polysaccharide in the case of apoemulsan to 370 U/mg protein/mg polysaccharide in the case of alginic acid. The stability of the emulsions ranged between 95 and 58%. Emulsions formed in the presence of seven of the polysaccharides exhibited stabilities of over 80%. The esterase from A. calcoaceticus BD4, which shows sequence homology to the RAG-1 esterase, was inactive in emulsification enhancement. The sequence of the RAG-1 esterase was shown to contain two conserved peptide sequences previously shown to be implicated in carbohydrate/polysaccharide binding. A hypothetical model illustrating a possible mode of interaction between the esterase, the apoemulsan and the oil droplet is presented. The complex is presumed to generate a series of "coated" oil droplets which are restricted in their ability to coalesce resulting in a relatively stable emulsion.
authors.affiliation: Department of Molecular Microbiology and Biotechnology, Faculty of Life Science, Tel Aviv University, Ramat Aviv, 69978, Israel.
authors.forename: Horacio
authors.initials: H
authors.lastname: Bach
authors.forename: David L
authors.initials: DL
authors.lastname: Gutnick
mesh_terms: D000150:Acinetobacter / Q000378:metabolism*; D000473:Alkanes / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000378:metabolism*; D004655:Emulsions / Q000737:chemistry / Q000378:metabolism; D004950:Esterases / Q000096:biosynthesis / Q000378:metabolism*; D007313:Insecta / Q000737:chemistry; D010944:Plants / Q000737:chemistry; D011134:Polysaccharides / Q000138:chemical synthesis / Q000378:metabolism*; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism
chemical_list: D000473:Alkanes; D001426:Bacterial Proteins; D004655:Emulsions; D011134:Polysaccharides; D011135:Polysaccharides, Bacterial; D011994:Recombinant Proteins; C036028:emulsan; D004950:Esterases; C007932:n-hexadecane