Increasing Immunogenicity of Antigens Fused to Ig-Binding Proteins by Cell Surface Targeting

Fusion of antigenic proteins to Ig-binding proteins such as protein A from Staphylococcus aureus and its derived ZZ fragment is known to increase immunogenicity of the fused Ag in vivo. To shed light on the origin of this effect, we used snake toxins as Ags and observed that 1) fusion of toxins to ZZ enhanced their presentation to a toxin-specific T cell hybridoma (T1B2), using A20 B lymphoma cells, splenocytes, or peritoneal exudate cells as APCs; 2) this enhancement further increased when the number of fused Ig-binding domains varied from two with ZZ to five with protein A; and 3) the phenomenon vanished when the fusion protein was preincubated with an excess of free ZZ or when P388D1 monocytes cells were used as APCs. Therefore, ZZ-fused toxins are likely to be targeted to surface Igs of APCs by their ZZ moiety. Furthermore, ZZ-α and toxin α stimulated similar profiles of toxin-specific T cells in BALB/c mice, suggesting a comparable processing and presentation in vivo for both toxin forms. To improve the targeting efficiency, ZZ-α was noncovalently complexed to various Igs directed to different cell surface components of APCs. The resulting complexes were up to 103-fold more potent than the free toxin at stimulating T1B2. Also, they elicited both a T cell and an Ab response in BALB/c mice, without the need of any adjuvant. This simple approach may find practical applications by increasing the immunogenicity of recombinant proteins without the use of adjuvant.

Increasing immunogenicity of antigens fused to Ig-binding proteins by cell surface targeting

Fusion of antigenic proteins to Ig-binding proteins such as protein A from Staphylococcus aureus and its derived ZZ fragment is known to increase immunogenicity of the fused Ag in vivo. To shed light on the origin of this effect, we used snake toxins as Ags and observed that 1) fusion of toxins to ZZ enhanced their presentation to a toxin-specific T cell hybridoma (T1B2), using A20 B lymphoma cells, splenocytes, or peritoneal exudate cells as APCs; 2) this enhancement further increased when the number of fused Ig-binding domains varied from two with ZZ to five with protein A; and 3) the phenomenon vanished when the fusion protein was preincubated with an excess of free ZZ or when P388D1 monocytes cells were used as APCs. Therefore, ZZ-fused toxins are likely to be targeted to surface Igs of APCs by their ZZ moiety. Furthermore, ZZ-alpha and toxin alpha stimulated similar profiles of toxin-specific T cells in BALB/c mice, suggesting a comparable processing and presentation in vivo for both toxin forms. To improve the targeting efficiency, ZZ-alpha was noncovalently complexed to various Igs directed to different cell surface components of APCs. The resulting complexes were up to 10(3)-fold more potent than the free toxin at stimulating T1B2. Also, they elicited both a T cell and an Ab response in BALB/c mice, without the need of any adjuvant. This simple approach may find practical applications by increasing the immunogenicity of recombinant proteins without the use of adjuvant.

A particularly labile Asp-Pro bond in the green mamba muscarinic toxin MTX2. Effect of protein conformation on the rate of cleavage

The single Asp53-Pro54 bond of the MTX2 toxin from the mamba snake Dendroaspis angusticeps is rapidly and efficiently cleaved in acidic solution (pH 1.5-2.5) at 45 degrees C. Unfolding of the toxin slows down the cleavage reaction by several times. Modelling studies indicate that the native toxin conformation can catalyse the Asp53-Pro54 bond cleavage. The implications of this study are: (i) cleavage of Asp-Pro bond for sequence determination may occur better in absence than in presence of denaturant, (ii) mild acid conditions, commonly used in NMR structure determinations, may irreversibly affect the structural integrity of Asp-Pro containing peptides and proteins.