Industrial Exploitation by Genetic Engineering of Bacterial Glycosylation Systems

Several bacterial species synthesize glycoproteins using oligosaccharyltransferases (OTases) that transfer glycans preassembled onto a lipid donor to proteins. To date, only three bacterial OTases (PglB, PilO, and PglL) have been characterized. The PglB protein is the OTase from Campylobacter jejuni involved in the N-glycosylation of multiple proteins. Likewise, PilO from Pseudomonas aeruginosa and PglL from Neisseria meningitidis are OTases responsible for pilin O-glycosylation in these bacteria. A common denominator of the three OTases is that they have relaxed glycan specificity, being able to transfer diverse glycans to proteins. The PglB protein presents the advantage that it is possible to adapt a nonglycosylated protein to be a glycan acceptor by simply adding the acceptor consensus sequence in a loop of the protein. These three OTases have been functionally expressed in Escherichia coli and exhibit relaxed glycan specificity, which opens the door to the possibility of engineering recombinant glycoproteins for biotechnological applications. Bacteria, in particular E. coli cells, constitute a perfect toolbox for glycoengineering, as they tolerate the incorporation and manipulation of foreign bacterial glycosylation pathways. The most promising application for this type of glycoproteins is the design and synthesis of a new generation of conjugate vaccines and glycan-based therapeutics.