Discovery of a single-subunit oligosaccharyltransferase that enables glycosylation of full-length IgG antibodies in .

Human immunoglobulin G (IgG) antibodies are one of the most important classes of biotherapeutic agents and undergo glycosylation at the conserved N297 site in the C2 domain, which is critical for IgG Fc effector functions and anti-inflammatory activity. Hence, technologies for producing authentically glycosylated IgGs are in high demand. While attempts to engineer for this purpose have been described, they have met limited success due in part to the lack of available oligosaccharyltransferase (OST) enzymes that can install linked glycans within the QYNST sequon of the IgG C2 domain.

Cell-Free Systems for the Production of Glycoproteins.

Cell-free protein synthesis (CFPS), whereby cell lysates are used to produce proteins from a genetic template, has matured as an attractive alternative to standard biomanufacturing modalities due to its high volumetric productivity contained within a distributable platform. Initially, cell-free lysates produced from Escherichia coli, which are both simple to produce and cost-effective for the production of a wide variety of proteins, were unable to produce glycosylated proteins as E. coli lacks native glycosylation machinery.

Ribosome Stalling of -Linked Glycoproteins in Cell-Free Extracts.

Ribosome display is a powerful method for selection and directed evolution of proteins expressed from combinatorial libraries. However, the ability to display proteins with complex post-translational modifications such as glycosylation is limited. To address this gap, we developed a set of complementary methods for producing stalled ribosome complexes that displayed asparagine-linked (-linked) glycoproteins in conformations amenable to downstream functional and glycostructural interrogation.

Three-dimensional structure-guided evolution of a ribosome with tethered subunits.

RNA-based macromolecular machines, such as the ribosome, have functional parts reliant on structural interactions spanning sequence-distant regions. These features limit evolutionary exploration of mutant libraries and confound three-dimensional structure-guided design. To address these challenges, we describe Evolink (evolution and linkage), a method that enables high-throughput evolution of sequence-distant regions in large macromolecular machines, and library design guided by computational RNA modeling to enable exploration of structurally stable designs.