title: A new cytolytic protein from the sea anemone Urticina crassicornis that binds to cholesterol- and sphingomyelin-rich membranes.
abstract: A new pore-forming cytolytic protein was isolated from the Northern red sea anemone, Urticina crassicornis. Its biochemical properties were characterized and partial N-terminal amino acid sequence was determined. The cytolysin, named UcI, has a molecular mass of around 30kDa and lacks phospholipase A(2) activity. UcI lyses bovine erythrocytes at nanomolar concentrations. Hemolysis is a result of a colloid-osmotic shock caused by the opening of toxin-induced ionic pores and can be prevented by osmotic protectants of size >600Da. The functional radius of an average pore was estimated to be about 0.66nm. A more detailed study of the cytolytic activity of UcI was performed with lipid vesicles and monolayers. The toxin binds to monolayers and efficiently permeabilizes small lipid vesicles composed of sphingomyelin and cholesterol. However, the cytolytic activity is not prevented by preincubation with either pure cholesterol or sphingomyelin dispersions. We conclude that the presence of both sphingomyelin and cholesterol, key components of lipid rafts, greatly enhances toxin binding to membranes and probably facilitates pore formation. Alignment of the toxin partial amino acid sequence with sequences of cytolysins belonging to the actinoporin family reveals no sequence homology. We conclude that partial sequence of UcI resembles only the N-terminal part of UpI, a cytolytic protein isolated from a related sea anemone species, Urticina piscivora. The two proteins most probably belong to a separate family of sea anemone cytolysins that are worthy of further characterization.
authors.affiliation: Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Andrej
authors.initials: A
authors.lastname: Razpotnik
authors.forename: Igor
authors.initials: I
authors.lastname: Krizaj
authors.forename: William R
authors.initials: WR
authors.lastname: Kem
authors.forename: Peter
authors.initials: P
authors.lastname: Macek
authors.forename: Tom
authors.initials: T
authors.lastname: Turk
mesh_terms: D000595:Amino Acid Sequence; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D002850:Chromatography, Gel; D003064:Cnidarian Venoms / Q000737:chemistry* / Q000201:enzymology / Q000302:isolation & purification / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D005612:Freeze Drying; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D008055:Lipids / Q000737:chemistry; D008566:Membranes / Q000378:metabolism; D008567:Membranes, Artificial; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009994:Osmolar Concentration; D010713:Phosphatidylcholines / Q000737:chemistry; D054467:Phospholipases A2 / Q000737:chemistry / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification; D013109:Sphingomyelins / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D003064:Cnidarian Venoms; D008055:Lipids; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D012333:RNA, Messenger; D013109:Sphingomyelins; C543525:UcI protein, Urticina crassicornis; D002784:Cholesterol; D054467:Phospholipases A2; C017251:1,2-oleoylphosphatidylcholine