Structural and Immunogenic Effects of Multiple Hapten Loading on Carrier Protein

Abstract

Haptens are low-molecular-weight compounds that are usually nonimmunogenic in nature. These compounds are, in general, conjugated with carrier proteins to elicit an immune response for antibody production. In this work, we report the effect of multiple hapten loading on carrier protein after conjugation by monitoring the structural and immunogenic properties of the protein. Biochemical conjugation of carboxylated hapten (atrazine derivative) to bovine serum albumin via epsilon-amino groups of lysine residues was monitored by the intrinsic fluorescence intensity of tryptophan residues of protein. A significant blue shift of emission maxima confirmed the conformational changes with increasing molar ratio of hapten:protein. Circular dichroism spectroscopy suggested a decreasing trend for alpha-helical and increased formation of beta-sheet structures in hapten-loaded protein. A further insight was sought by using molecular modeling methods for understanding of structural changes in the native protein post-hapten conjugation. A sequential approach for hapten loading on the carrier confirmed that initial binding could affect the possible binding sites for subsequent incorporation of hapten molecules. These changes play a major role in the immunogenic response of hapten-carrier conjugate. The approach taken to develop this model is promising, and can be generalized for studies with other protein-hapten combinations.