The human-specific action of intermedilysin, a homolog of streptolysin O, is dictated by domain 4 of the protein.
Intermedilysin is a pore-forming cytolysin belonging to the streptolysin O gene family known as the 'Cholesterol-binding/dependent cytolysins' and is unique within the family in that it is highly humanspecific. This specificity suggests interaction with a component of human cells other than cholesterol, the proposed receptor for the other toxins of the gene family. Indeed, intermedilysin showed no significant degree of affinity to free or liposome-embedded cholesterol. Characterization of intermedilysin undecapeptide mutants revealed that this lack of affinity to cholesterol was a result of the substitutions of intermedilysin in this region. Absorption assays with erythrocyte membranes from various animals, competitive inhibition with domain 4 of intermedilysin and liposome-binding assays of streptolysin O and intermedilysin indicated that cell membrane binding is the human-specific step of intermedilysin action, that the host cell membrane-binding site is located within domain 4 in common with other members of the family and that the receptor for this toxin is not cholesterol. The species specificity of undecapeptide mutants of intermedilysin and streptolysin O and chimeric mutants between intermedilysin and streptolysin O, and intermedilysin and pneumolysin indicated that domain 4 of intermedilysin determines the human-specific action step and the cell-binding site of domain 4 lies within the 56 amino acids of the C-terminal, excluding the undecapeptide region.
Nagamune
Hideaki
H
Department of Biological Science and Technology, Faculty of Engineering, The University of Tokushima, #1, 2-chrome, Minamijosanjima-cho, Tokushima, Tokushima 770-8506, Japan. nagamune@bio.tokushima-u.ac.jp
Ohkura
Kazuto
K
Sukeno
Akiko
A
Cowan
Graeme
G
Mitchell
Timothy J
TJ
Ito
Wataru
W
Ohnishi
Ooki
O
Hattori
Kanako
K
Yamato
Miki
M
Hirota
Katsuhiko
K
Miyake
Yoichiro
Y
Maeda
Takuya
T
Kourai
Hiroki
H
D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001430:Bacteriocins; D001665:Binding Sites; D002784:Cholesterol / Q000378:metabolism; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006461:Hemolysis; D006801:Humans; D008081:Liposomes; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017354:Point Mutation; D011817:Rabbits; D013045:Species Specificity; D034367:Streptococcus intermedius / Q000235:genetics / Q000378:metabolism*; D013301:Streptolysins / Q000235:genetics
D001426:Bacterial Proteins; D001430:Bacteriocins; D008081:Liposomes; D013301:Streptolysins; C403910:intermedilysin protein, Streptococcus intermedius; C025964:streptolysin O; D002784:Cholesterol