Allosteric deimmunisation of a Salmonella phosphatase enhances catalytic function

Abstract

Genetically engineered Salmonella strains are promising vectors for cancer therapy, but their clinical use is limited by host immune responses. A key immunogenic antigen, the phosphatase PhoN, is metabolically essential for bacterial survival in the vitamin B6-depleted tumour microenvironment and thus cannot be simply deleted. While conventional deimmunisation targets surface residues, we present a strategy of allosteric deimmunisation by mutating non-surface, buried residues within the dominant h2 helix T-cell epitope. We hypothesised that the epitope is allosterically coupled to the distal active site gate, allowing for the simultaneous modulation of immunogenicity and enzymatic function. Using a computational pipeline, we designed deimmunised variants and used molecular dynamics (MD) simulations to predict their functional effects. The simulations revealed that mutations in the h2 helix allosterically controlled the gates flexibility. The enzymatic activities of the deimmunized variants were correlated with the MD predictions: two of the five designed variants exhibited 2[~]3-fold increases in catalytic function. This work demonstrates that non-surface epitopes can be rationally engineered to not only ablate immunogenicity but also to allosterically enhance protein function.