The role of structural domains in RIP II toxin model membrane binding.
The interaction of plant toxin ricin and MLI binding subunits to liposomes containing monosialoganglioside (GM1), bearing a terminal galactose residue, has been examined as a possible receptor model. For the first time we demonstrate that ricin B-chain but not ricin provokes liposome aggregation at 10 M% GM1 concentration, whereas in the presence of either ricin A-chain or galactose the aggregation is inhibited. The B-subunit of plant toxin MLI from Viscum album has similar lectin specificity and activity but cannot aggregate GM1 liposomes. The ability of the B-chain to aggregate liposomes adds a new crucial step in the toxin transmembrane penetration mechanism. We demonstrate here possible ricin B-chain interactions with membranes proceeding via two sites, namely (a) a galactose-binding domain and (b) a hydrophobic interchain domain. In close contact with two phospholipid bilayers, ricin B-chain may determine the geometry of the fusion site. These events can provoke A-chain translocation which follows membrane fusion.
Agapov
I I
II
State Scientific Center for Genetics and Selection of Microorganisms, GosNIIGENETIKA, Moscow, Russian Federation.
Tonevitsky
A G
AG
Shamshiev
A T
AT
Pohl
E
E
Pohl
P
P
Palmer
R A
RA
Kirpichnikov
M P
MP
D001665:Binding Sites; D002470:Cell Survival / Q000187:drug effects; D004134:Dimyristoylphosphatidylcholine; D005677:G(M1) Ganglioside; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019169:Jurkat Cells; D008051:Lipid Bilayers; D008081:Liposomes / Q000378:metabolism*; D028321:Plant Preparations; D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D012276:Ricin / Q000737:chemistry / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D014118:Toxins, Biological / Q000737:chemistry / Q000378:metabolism*
D008051:Lipid Bilayers; D008081:Liposomes; D028321:Plant Preparations; D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological; C009674:ribosome inactivating protein, Viscum; D005677:G(M1) Ganglioside; D012276:Ricin; D004134:Dimyristoylphosphatidylcholine