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Chemical approaches to perturb, profile, and perceive glycans.

Agard NJ, Bertozzi CR - Acc. Chem. Res. (2009)

Bottom Line: Together, glycomic and metabolic labeling techniques provide a comprehensive description of glycosylation as a foundation for hypothesis generation.Fluorescent tagging in cultured cells and developing organisms has revealed important insights into the dynamics of these structures during growth and development.These results have highlighted the need for additional imaging probes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of California, Berkeley, USA.

ABSTRACT
Glycosylation is an essential form of post-translational modification that regulates intracellular and extracellular processes. Regrettably, conventional biochemical and genetic methods often fall short for the study of glycans, because their structures are often not precisely defined at the genetic level. To address this deficiency, chemists have developed technologies to perturb glycan biosynthesis, profile their presentation at the systems level, and perceive their spatial distribution. These tools have identified potential disease biomarkers and ways to monitor dynamic changes to the glycome in living organisms. Still, glycosylation remains the underexplored frontier of many biological systems. In this Account, we focus on research in our laboratory that seeks to transform the study of glycan function from a challenge to routine practice. In studies of proteins and nucleic acids, functional studies have often relied on genetic manipulations to perturb structure. Though not directly subject to mutation, we can determine glycan structure-function relationships by synthesizing defined glycoconjugates or by altering natural glycosylation pathways. Chemical syntheses of uniform glycoproteins and polymeric glycoprotein mimics have facilitated the study of individual glycoconjugates in the absence of glycan microheterogeneity. Alternatively, selective inhibition or activation of glycosyltransferases or glycosidases can define the biological roles of the corresponding glycans. Investigators have developed tools including small molecule inhibitors, decoy substrates, and engineered proteins to modify cellular glycans. Current approaches offer a precision approaching that of genetic control. Genomic and proteomic profiling form a basis for biological discovery. Glycans also present a rich matrix of information that adapts rapidly to changing environs. Glycomic and glycoproteomic analyses via microarrays and mass spectrometry are beginning to characterize alterations in glycans that correlate with disease. These approaches have already identified several cancer biomarkers. Metabolic labeling can identify recently synthesized glycans and thus directly track glycan dynamics. This approach can highlight changes in physiology or environment and may be more informative than steady-state analyses. Together, glycomic and metabolic labeling techniques provide a comprehensive description of glycosylation as a foundation for hypothesis generation. Direct visualization of proteins via the green fluorescent protein (GFP) and its congeners has revolutionized the field of protein dynamics. Similarly, the ability to perceive the spatial organization of glycans could transform our understanding of their role in development, infection, and disease progression. Fluorescent tagging in cultured cells and developing organisms has revealed important insights into the dynamics of these structures during growth and development. These results have highlighted the need for additional imaging probes.

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Examples of glycoconjugates. Many proteins are glycosylated at asparagine (N-linked) or serine/threonine residues (mucin-type O-linked and O-GlcNAc are shown). Lipids, secondary metabolites, and tRNA are examples of other biomolecules found in glycosylated form.
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fig1: Examples of glycoconjugates. Many proteins are glycosylated at asparagine (N-linked) or serine/threonine residues (mucin-type O-linked and O-GlcNAc are shown). Lipids, secondary metabolites, and tRNA are examples of other biomolecules found in glycosylated form.

Mentions: Virtually every class of biomolecule can be found in a glycosylated form. This phenomenon extends from the glycoproteins, which we now know comprise ∼50% of the total cellular proteome and >90% of the secreted proteome,1,2 to lipids, tRNA,(3) and many secondary metabolites (Figure 1). But the question, “what do the glycans do?” remains unanswered in many cases. Decades of research in the rapidly expanding field of glycobiology have provided some insights. For example, glycans have been shown to govern biological homeostasis, playing central roles in protein folding, trafficking, and stability,(4) and in organ development.(5) Inside cells, protein glycosylation is thought to play a role in signaling, perhaps in concert with phosphorylation.(6) Cell-surface glycans are poised to mediate intercellular communication,(7) including pathogen recognition,8,9 and to distinguish self from non-self immunologically.(10) In addition, the glycosylation state of both cell-surface proteins and lipids responds to external stimuli and internal cellular dysfunction. Thus, the dynamics of these molecules reflect the cell’s physiological state and can report on disease.(11)


Chemical approaches to perturb, profile, and perceive glycans.

Agard NJ, Bertozzi CR - Acc. Chem. Res. (2009)

Examples of glycoconjugates. Many proteins are glycosylated at asparagine (N-linked) or serine/threonine residues (mucin-type O-linked and O-GlcNAc are shown). Lipids, secondary metabolites, and tRNA are examples of other biomolecules found in glycosylated form.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2697281&req=5

fig1: Examples of glycoconjugates. Many proteins are glycosylated at asparagine (N-linked) or serine/threonine residues (mucin-type O-linked and O-GlcNAc are shown). Lipids, secondary metabolites, and tRNA are examples of other biomolecules found in glycosylated form.
Mentions: Virtually every class of biomolecule can be found in a glycosylated form. This phenomenon extends from the glycoproteins, which we now know comprise ∼50% of the total cellular proteome and >90% of the secreted proteome,1,2 to lipids, tRNA,(3) and many secondary metabolites (Figure 1). But the question, “what do the glycans do?” remains unanswered in many cases. Decades of research in the rapidly expanding field of glycobiology have provided some insights. For example, glycans have been shown to govern biological homeostasis, playing central roles in protein folding, trafficking, and stability,(4) and in organ development.(5) Inside cells, protein glycosylation is thought to play a role in signaling, perhaps in concert with phosphorylation.(6) Cell-surface glycans are poised to mediate intercellular communication,(7) including pathogen recognition,8,9 and to distinguish self from non-self immunologically.(10) In addition, the glycosylation state of both cell-surface proteins and lipids responds to external stimuli and internal cellular dysfunction. Thus, the dynamics of these molecules reflect the cell’s physiological state and can report on disease.(11)

Bottom Line: Together, glycomic and metabolic labeling techniques provide a comprehensive description of glycosylation as a foundation for hypothesis generation.Fluorescent tagging in cultured cells and developing organisms has revealed important insights into the dynamics of these structures during growth and development.These results have highlighted the need for additional imaging probes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of California, Berkeley, USA.

ABSTRACT
Glycosylation is an essential form of post-translational modification that regulates intracellular and extracellular processes. Regrettably, conventional biochemical and genetic methods often fall short for the study of glycans, because their structures are often not precisely defined at the genetic level. To address this deficiency, chemists have developed technologies to perturb glycan biosynthesis, profile their presentation at the systems level, and perceive their spatial distribution. These tools have identified potential disease biomarkers and ways to monitor dynamic changes to the glycome in living organisms. Still, glycosylation remains the underexplored frontier of many biological systems. In this Account, we focus on research in our laboratory that seeks to transform the study of glycan function from a challenge to routine practice. In studies of proteins and nucleic acids, functional studies have often relied on genetic manipulations to perturb structure. Though not directly subject to mutation, we can determine glycan structure-function relationships by synthesizing defined glycoconjugates or by altering natural glycosylation pathways. Chemical syntheses of uniform glycoproteins and polymeric glycoprotein mimics have facilitated the study of individual glycoconjugates in the absence of glycan microheterogeneity. Alternatively, selective inhibition or activation of glycosyltransferases or glycosidases can define the biological roles of the corresponding glycans. Investigators have developed tools including small molecule inhibitors, decoy substrates, and engineered proteins to modify cellular glycans. Current approaches offer a precision approaching that of genetic control. Genomic and proteomic profiling form a basis for biological discovery. Glycans also present a rich matrix of information that adapts rapidly to changing environs. Glycomic and glycoproteomic analyses via microarrays and mass spectrometry are beginning to characterize alterations in glycans that correlate with disease. These approaches have already identified several cancer biomarkers. Metabolic labeling can identify recently synthesized glycans and thus directly track glycan dynamics. This approach can highlight changes in physiology or environment and may be more informative than steady-state analyses. Together, glycomic and metabolic labeling techniques provide a comprehensive description of glycosylation as a foundation for hypothesis generation. Direct visualization of proteins via the green fluorescent protein (GFP) and its congeners has revolutionized the field of protein dynamics. Similarly, the ability to perceive the spatial organization of glycans could transform our understanding of their role in development, infection, and disease progression. Fluorescent tagging in cultured cells and developing organisms has revealed important insights into the dynamics of these structures during growth and development. These results have highlighted the need for additional imaging probes.

Show MeSH
Related in: MedlinePlus