-C1q410,0001w -C1s87.000Hw 190.000Hw CI recognition complex Tw laG molecules Or one IgM molecule binding to antibody. CIs become an active enzyme(esterase) substrate. Structure of the Cl Molecule.The Cl protein is composed of three proteins:Clq,which binds to the Fc portion of the Ab molecule;Cls,which can enzymatically cleave the next complement component,C4:and CIr,which acts as a bridge connecting Clq to Cls.Structure of the C1 Molecule. The C1 protein is composed of three proteins: C1q, which binds to the Fc portion of the Ab molecule; C1s, which can enzymatically cleave the next complement component, C4; and C1r, which acts as a bridge connecting C1q to C1s