Life is governed by a repertoire of key chemical transformations. Cells, both prokaryotic and eukaryotic, are probably the most advanced molecular factories one can imagine. Could chemists improve this machinery? Maybe. Could chemists expand the properties of these cellular systems? Most definitely. Advances in bioorthogonal chemistry already proved that non-native reactions can be a great tool to study biological processes. Performing new-to-nature chemistry at a cellular level could be key to the engineering of biological functions. Think of a cellular system where an abiotic bond-breaking reaction could selectively activate a molecule of interest (e.g. a prodrug or a reporter). This approach could be leveraged to manipulate biological processes with applications ranging from diagnosis to innovative therapies. Most approaches for the activation of probes or prodrugs in cellulo rely on the direct incubation of cells with metal complexes or nanoparticles. Aspects such as the localization of the metal or the delivery of the metal complexes raise the question of the applicability of this strategy.
In this context, we wondered whether we could implement an artificial metalloenzyme functioning as a “chemical prosthesis” on the surface of live cells. What followed is the result of a truly interdisciplinary team effort.
An artificial metalloenzyme capable of catalyzing the cleavage of allyl-carbamate protected amines was first developed. The artificial allylic deallylase, based on the biotin-streptavidin technology, was then optimized by screening of streptavidin mutants obtained by site-directed mutagenesis. A workflow for the surface functionalization of Chlamydomonas reinhardtii with the artificial metalloenzyme was then developed. The engineered cells were able to uncage a fluorogenic substrate on their surface with preserved cell viability.
This work shows that it is possible to endow live cells with new reactivity by installing a tailor-made artificial metalloenzyme on their surface. Streptavidin functions both as the host protein of the metalloenzyme and the anchoring strategy. This approach is versatile as artificial metalloenzymes with different reactivities could be installed on the cell surface following the same method. The concept introduced in this work could pave the way for further applications in term of prodrug activation. For example, one can imagine endowing cancer cells with the ability to uncage anticancer prodrugs by cell surface engineering with such chemical prosthesis.