Siderophores as anchors in artificial metalloenzymes

The project involves the development of artificial metalloenzymes that consist of a synthetic catalytic centre that is linked via an anchor group to a protein that acts as a scaffold. This design allows the combination of the chemical reactivity of organometallic catalysts with the selectivity and biocompatibility of proteins. Such artificial enzymes would allow existing catalytic processes to run under mild conditions and make new biotechnological transformations possible. In addition, such artificial enzymes could be used to activate antibiotics.

The anchor groups to be investigated in this project are based on siderophores, which are ligands that are produced by bacteria for the uptake of essential iron. The iron(III)-siderophore complexes formed are extremely stable and actively transported into the bacterial cell. In Gram-negative bacteria, transport involves recognition and uptake via a specific outer membrane receptor, followed by capture by a periplasmic binding protein and delivery to an inner membrane transporter for translocation into the cytoplasm.

It is the periplasmic siderophore binding proteins that will be explored as novel protein scaffolds in artificial enzymes. The advantage of this approach is the active transport of the synthetic catalysts into the bacterial cell via the siderophore uptake system. Once the catalysts are taken-up along with the iron siderophore complexes, they are captured by their respective binding proteins. Hence the target artificial enzymes self-assemble and accumulate in the periplasm of the bacterial cell, where they may be used for catalytic transformations or the activation of antimicrobial prodrugs. In this way, by taking advantage of the bacterial iron-uptake pathway that is mediated by siderophores, the metabolism of the bacterial cell is exploited to support chemical transformations in vivo.

In addition to the immediate benefit of advancing the development of artificial enzymes, the proposed work may lead to the development of new catalysts with the potential to improve the biocompatibility of industrially relevant processes. In addition, our approach may enable the development of catalysts for transformations that have no equivalent either in homogeneous or enzymatic catalysis or the running of existing catalytic processes in a more sustainable way. A particular strength of the proposed protein-based catalysts lies in the preparation of enantiomerically pure molecules.

Furthermore, the proposed work may lead to the development of novel antimicrobial prodrugs. With the current lack of industrial research in the area of antimicrobials and bacterial resistance on the rise, it is particularly important that academics contribute to the field. We anticipate that the insights generated and researchers trained through our research will strengthen antimicrobial research nationally and internationally and that our publications will help to inform policy-makers. In the long-term, the proposed research could improve the health and quality of life of patients, if successful. In particular prodrugs that delay the development of resistance would be highly beneficial, since drug resistance tends to prolong the duration of an infection.

The proposal is thus relevant to several areas identified as of strategic importance by the research councils, including manufacturing for the future, catalysis, frontier manufacturing, sustainable industrial systems and the EPSRC challenge theme healthcare technologies.

Hence, the work could have considerable economic and societal impact in the long-term. In order to ensure the commercial potential of promising catalysts or antimicrobials, we will seek both intellectual property (IP) protection and industrial expertise. Help will be provided by the University of York Enterprise and Innovation Office. Once IP protection has been obtained, the results obtained will be published as communications and as full papers. In addition, lectures and posters will be presented at conferences and during visits to research institutions.

Since the move towards greener chemical technology is of much current interest and importance, the proposed work provides an opportunity to engage with the public and to raise awareness of environmental and sustainability issues. In addition, we believe that it is important to inform the public better about the problem of antibiotic resistance. The PI has already published an article in Education in Chemistry on the use of siderophores in antimicrobials, given a public lecture on the subject, and talked at schools events. In addition, we have offered many undergraduate projects on antibiotic research over the past five years, which proved to be very successful. We intend to continue and extend these and related outreach activities further.

The work will result in the training of highly skilled PDRAs, who will be well prepared for employment in either the academic and industrial sector. In addition, new graduates and final year undergraduates working on related projects will benefit from the training provided.