Asparagine-linked protein glycosylation is involved in a wide range of biological processes that are implicated in human health and disease. The modification is essential in all aspects of human development and homeostasis and now recognized to be involved in bacterial pathogenicity and viral infection and survival. N-linked glycosylation is also of great relevance in medicine and biotechnology, as protein therapeutics including monoclonal antibodies, glycoprotein hormones, and cytokines have become important elements in the modern pharmacopoeia. While the specific biological functions and the molecular details of N-linked glycosylation in bacteria and man vary, there are key conserved elements in the overall processes that support the hypothesis that the detailed study of the prokaryotic protein glycosylation (pgl) pathway of C. jejuni, which forms the basis for this research, will also provide insight into the more complex process of N-linked glycosylation in eukaryotes. The biosynthetic pathways that lead to N-linked glycosylation in all organisms involve multistep membrane- associated processes and feature complex highly lipophilic polyprenol-linked substrates. These characteristics pose major challenges as we seek to develop a detailed molecular understanding of how the enzymes in these pathways come together to afford the ordered biosynthetic assembly line that ultimately yields essential N-linked glycoproteins. Until we understand the relationships amongst the polyprenol-linked substrates, the enzymes that process them and the membrane bilayer in which they are localized, we will be limited in our ability to target the constituent processes to mitigate disease and to exploit th pathways to generate glycoproteins that might be relevant as therapeutic biologicals. The proposed research centers on the application of synergistic in vitro and in vivo biochemical and biophysical approaches for investigating bacterial N-linked protein glycosylation.
The aims of the proposal are: 1. To investigate the structural and functional interactions of the five pgl pathway glycan assembly enzymes in a Nanodisc model membrane system and to define the functional significance of conserved linear long-chain polyprenyl moieties in the substrates of the pathway enzymes. 2. To apply in vivo fluorescence-based imaging to correlate findings from the interaction analysis in the in vitro model membrane with studies in E. coli where the pgl pathway has been functionally reconstituted. 3. To define the interactions of the OTase, PglB with cognate substrates in vitro in Nanodisc membranes and in vivo with the membrane-associated proteins of the pgl pathway and the bacterial translocon. If the goals of the proposed research are achieved, the research will result in the development of general strategies for dissecting related membrane-associated polyprenol-dependent biosynthetic processes that feature prominently in all living systems.

Public Health Relevance

Many essential multistep biochemical processes in nature occur at cellular membranes;however, because of the technical difficulties associated with studying these systems, their detailed understanding remains elusive. Recent research has defined the individual steps that are involved in the production of cell surface glycoproteins and glycolipids, but we are far from understanding how the individual transformations come together as a whole to afford an efficient and quality-controlled pathway. Our proposed studies seek to fill this gap in knowledge by developing a new strategic approach for studying the polyprenol-dependent multicomponent glycoprotein assembly pathways, that are highly conserved and essential elements in eukaryotic development and homeostasis as well as microbial pathogenesis.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Synthetic and Biological Chemistry B Study Section (SBCB)
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Gerratana, Barbara
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Massachusetts Institute of Technology
Schools of Arts and Sciences
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Larkin, Angelyn; Chang, Michelle M; Whitworth, Garrett E et al. (2013) Biochemical evidence for an alternate pathway in N-linked glycoprotein biosynthesis. Nat Chem Biol 9:367-73
Jaffee, Marcie B; Imperiali, Barbara (2013) Optimized protocol for expression and purification of membrane-bound PglB, a bacterial oligosaccharyl transferase. Protein Expr Purif 89:241-50
Larkin, Angelyn; Imperiali, Barbara (2011) The expanding horizons of asparagine-linked glycosylation. Biochemistry 50:4411-26
Hartley, Meredith D; Morrison, Michael J; Aas, Finn Erik et al. (2011) Biochemical characterization of the O-linked glycosylation pathway in Neisseria gonorrhoeae responsible for biosynthesis of protein glycans containing N,N'-diacetylbacillosamine. Biochemistry 50:4936-48
Jaffee, Marcie B; Imperiali, Barbara (2011) Exploiting topological constraints to reveal buried sequence motifs in the membrane-bound N-linked oligosaccharyl transferases. Biochemistry 50:7557-67
Morrison, James P; Troutman, Jerry M; Imperiali, Barbara (2010) Development of a multicomponent kinetic assay of the early enzymes in the Campylobacter jejuni N-linked glycosylation pathway. Bioorg Med Chem 18:8167-71
Larkin, Angelyn; Imperiali, Barbara (2009) Biosynthesis of UDP-GlcNAc(3NAc)A by WbpB, WbpE, and WbpD: enzymes in the Wbp pathway responsible for O-antigen assembly in Pseudomonas aeruginosa PAO1. Biochemistry 48:5446-55
Troutman, Jerry M; Imperiali, Barbara (2009) Campylobacter jejuni PglH is a single active site processive polymerase that utilizes product inhibition to limit sequential glycosyl transfer reactions. Biochemistry 48:2807-16
Reid, Christopher W; Stupak, Jacek; Chen, Mark M et al. (2008) Affinity-capture tandem mass spectrometric characterization of polyprenyl-linked oligosaccharides: tool to study protein N-glycosylation pathways. Anal Chem 80:5468-75
Hartley, Meredith D; Larkin, Angelyn; Imperiali, Barbara (2008) Chemoenzymatic synthesis of polyprenyl phosphates. Bioorg Med Chem 16:5149-56

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