The cleavage of two C1s subunits by a single active C1r reveals substantial flexibility of the C1s-C1r-C1r-C1s tetramer in the C1 complex.
The activation of the C1s-C1r-C1r-C1s tetramer in the C1 complex, which involves the cleavage of an Arg-Ile bond in the catalytic domains of the subcomponents, is a two-step process. First, the autolytic activation of C1r takes place, then activated C1r cleaves zymogen C1s. The Arg463Gln mutant of C1r (C1rQI) is stabilized in the zymogen form. This mutant was used to form a C1q-(C1s-C1rQI-C1r-C1s) heteropentamer to study the relative position of the C1r and C1s subunits in the C1 complex. After triggering the C1 by IgG-Sepharose, both C1s subunits are cleaved by the single proteolytically active C1r subunit in the C1s-C1rQI-C1r-C1s tetramer. This finding indicates that the tetramer is flexible enough to adopt different conformations within the C1 complex during the activation process, enabling the single active C1r to cleave both C1s, the neighboring and the sequentially distant one.
Lörincz
Z
Z
Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest, Hungary.
Gál
P
P
Dobó
J
J
Cseh
S
S
Szilágyi
K
K
Ambrus
G
G
Závodszky
P
P
D000818:Animals; D001120:Arginine / Q000235:genetics; D003167:Complement Activation / Q000235:genetics; D015923:Complement C1r / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003173:Complement C1s / Q000737:chemistry / Q000378:metabolism*; D019281:Dimerization; D004792:Enzyme Precursors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005822:Genetic Vectors; D005973:Glutamine / Q000235:genetics; D006801:Humans; D006868:Hydrolysis; D016297:Mutagenesis, Site-Directed; D017924:Nucleopolyhedroviruses / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D018411:Spodoptera / Q000235:genetics
D004792:Enzyme Precursors; D011994:Recombinant Proteins; D005973:Glutamine; D001120:Arginine; D015923:Complement C1r; D003173:Complement C1s