ABSTRACT
The complement classical pathway is activated by the immunoglobulin M and immunoglobulin G antibody classes; therefore, their structures are relevant to complement. Antibodies based on chimeras with complement proteins have therapeutic value. An understanding of the solution structure of the hinges connecting the Fab and Fc fragments in different antibody classes is relevant to the design of the therapeutics. The first neutron-scattering studies on complement were performed with the heterotetramer C1r2C1s2 in both its activated and unactivated forms. C1 inhibitor forms stoichiometric complexes with C1r and C1s in order to control the activation of C1. Sedimentation coefficients from the literature for the complexes formed between C1 inhibitor, C1r, and C1s were analyzed using the combination of a two-domain head-and-tail model for C1 inhibitor and cylindrical models for C1r and C1s. The short consensus/complement repeat domain is the most abundant domain type in complement.
