1). Although unusual, the clonal origin of an antibody containing two separate light chains has been reported

earlier [52] and [53]. Thus, it seems that mAb selleck 67.5 may belong to such a category. All the four antibodies bound to VCP in a direct ELISA (data not shown). Since surface plasmon resonance (SPR) offers more quantitative data on biomolecule interactions, we utilized this method to measure the affinities of these antibodies. In the SPR setup, the antibodies were immobilized onto the chip and rVCP was flowed over it to measure binding. All the antibodies bound to VCP in a dose dependent manner (Fig. 1). The equilibrium dissociation constant (KD) of mAbs 67.5 and 67.9 (5.35 × 10−9 M and 6.6 × 10−9 M) was lower compared to those of 67.11 (4.64 × 10−8 M) and 67.13 (2.32 × 10−7 M), respectively ( Table 1). Interestingly, in a dot blot assay, these mAbs bound to VCP only under non-reducing conditions (data not shown) indicating that these antibodies recognize the conformational epitopes on VCP. To identify the VCP domains to which these mAbs buy SB431542 bind we performed an indirect ELISA using various truncation mutants of VCP (CCP 1–3, CCP 2–4, CCP 1–2, CCP 2–3 and CCP 3–4) that were expressed earlier in our laboratory using the Pichia expression system [42]. These expressed mutants were designed in

such a way that they started with the first Cys of the domain of interest and ended with the last residue of the inter-domain linker. Thus, this design kept the entire linker region at the C-terminal side of each of the mutants. The mAbs 67.5 and 67.9 reacted with CCP 1–3,

CCP 2–4, CCP 2–3 and CCP 3–4 mutants ( Fig. 2A and B) indicating that they recognize either domain 3 or the linker between domains 3 and 4 ( Fig. 2F). The antibodies 67.11 and 67.13 on the other hand reacted only with truncation mutants CCP 2–4 and CCP 3–4 ( Fig. 2C and D). Since the latter two antibodies did not show binding found to CCP 1–3, CCP 1–2 or CCP 2–3 it indicates that the binding epitopes for these antibodies lie on CCP domain 4 ( Fig. 2F). One of the functions of VCP is to serve as a cofactor for the complement specific serine protease factor I to mediate the inactivation of C3b (composed of α′ and β chains) and C4b (composed of α′, β and γ chains), the non-catalytic subunits of C3-convertases, which are the key enzymes in activation of the complement cascades. This function results in the cleavage of the α′-chains of C3b and C4b leading to the generation of their inactivated forms (iC3b or C4c and C4d) which can no longer participate in the formation of C3-convertases. As expected, incubation of rVCP or human factor H (control) with C3b and factor I resulted in cleavage of α′-chain of C3b (Fig. 3A). Similarly, incubation of rVCP or human sCR1 (control) with C4b and factor I resulted in cleavage of α′-chain of C4b (Fig. 3B).