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Báo cáo khoa học: The equinatoxin N-terminus is transferred across planar lipid membranes and helps to stabilize the transmembrane pore
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Equinatoxin II is a cytolytic protein isolated from the sea anemoneActi-nia equina. It is a member of the actinoporins, a family of eukaryotic pore-forming toxins with a unique mechanism of pore formation. Equinatoxin II is a 20 kDa cysteineless protein, with sphingomyelin-dependent activity. Recent studies showed that the N-terminal region of the molecule requires conformational flexibility during pore formation. | ỊFEBS Journal The equinatoxin N-terminus is transferred across planar lipid membranes and helps to stabilize the transmembrane pore Katarina Kristan1 Gabriella Viero2 Peter Macek1 Mauro Dalla Serra2 and Gregor Anderluh1 1 Department of Biology BiotechnicalFaculty University of Ljubljana Ljubljana Slovenia 2 ITC-CNR Institute of Biophysics Unit at Trento Trento Italy Keywords actinoporin equinatoxin planar lipid membrane pore-forming toxin pore structure Correspondence M. Dalla Serra ITC-CNR Institute of Biophysics Unit at Trento Via Sommarive 18 38050 Povo Trento Italy Fax 39 0461 810628 Tel 39 0461 314156 E-mail mdalla@itc.it G. Anderluh Department of Biology BiotechnicalFaculty University of Ljubljana Vecna pot 111 1000 Ljubljana Slovenia Fax 386 1 257 3390 Tel 386 1 42 333 88 E-mail gregor.anderluh@bf.uni-lj.si Received 27 August 2006 revised 11 November 2006 accepted 21 November 2006 doi 10.1111 j.1742-4658.2006.05608.x Equinatoxin II is a cytolytic protein isolated from the sea anemone Actinia equina. It is a member of the actinoporins a family of eukaryotic poreforming toxins with a unique mechanism of pore formation. Equinatoxin II is a 20 kDa cysteineless protein with sphingomyelin-dependent activity. Recent studies showed that the N-terminal region of the molecule requires conformational flexibility during pore formation. An understanding of the N-terminal position in the final pore and its role in membrane insertion and pore stability is essential to define the precise molecular mechanism of pore formation. The formation of pores and their electrophysiologic characteristics were studied with planar lipid membranes. We show that amino acids at positions 1 and 3 of equinatoxin II are exposed to the lumen of the pore. Moreover sulfhydryl reagents and a hexa-histidine tag attached to the N-terminus revealed that the N-terminus of the toxin extends through the pore to the other trans side of the membrane and that negatively charged residues inside the pore are