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| Towards the Enzymatic Synthesis of Carbohydrates |
| Li Cai* |
| Department of Chemistry, University of South Carolina Salkehatchie, USA |
| *Corresponding author: |
Dr. Li Cai
Department of Chemistry
University of South
Carolina Salkehatchie
Walterboro, SC 29488, USA
Tel: 843-549-6314 (Ext. 381)
E-mail: CAILI@mailbox.sc.edu |
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| Received March 03, 2012; Accepted March 06, 2012; Published March 10, 2012 |
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| Citation:Cai L (2012) Towards the Enzymatic Synthesis of Carbohydrates.
Organic Chem Current Res 1:e103. doi:10.4172/2161-0401.1000e103 |
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| Copyright: © 2012 Cai L. This is an open-access article distributed under the
terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited. |
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| Editorial |
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| Three major repeating biomacromolecules, nucleic acid, protein,
and carbohydrate carry out most of the information transfer in living
systems. Nucleic acid carries genetic information in the form of
DNA and RNA; PCR (Polymerase Chain Reaction), a revolutionary
technique developed in 1983 by K. Mullis, has become an indispensable
tool in biological and biomedical researches for nucleic acid synthesis.
On the other hand, solid-phase peptide synthesis, pioneered by R.
B. Merrifield, allows preparation of desired peptides and proteins in
vitro in a synthetic manner. However, due to the non-template based
biosynthetic pathway of carbohydrates, access structurally defined
homogeneous carbohydrate oligomers remains challenging when
automated synthesis of oligonucleotides and oligopeptides is common. |
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| Inventing new glycosylation reactions has been a long-standing
passion for organic and carbohydrate chemists because carbohydrates
represent a class of biopolymers which come in a far greater diversity
of structures: branching character, stereochemical issue, various types
of glycosidic bonds, and posttranslational modifications. A better
understanding of the structures of naturally occurring oligosaccharides
provides important information on the composition, linkage, branching
type of these oligomers [1]. Key building blocks could thus be designed
with appropriate protection groups to ensure desired linkage, branch
and anomeric selectivity/specificity. With the development of modern
organic chemistry, most naturally occurring oligosaccharides and
glycoconjugates are synthetically available. However, these chemical
approaches are hindered by tedious and time consuming protection and
deprotection steps, unsatisfactory stereoselectivities, and low overall
yields, making it impractical to prepare long-chain oligosaccharides
and polysaccharides. |
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| Bioorganic chemistry, the topic of a special issue of Organic
Chemistry: Current Research, addresses exactly this difficulty, with
reactions catalyzed by carbohydrate processing enzymes found in
nature. Dating back half a century, this field was initiated with the
growing understanding of sugar biosynthetic pathways [2] and the
corresponding key enzymes: glycosyltransferases, glycosidases and their
mutants. Though different enzymes utilize distinct donor molecules
(e.g. sugar nucleotide, nitrophenyl glycoside, glycosylfluoride) and
follow different mechanisms, the concept of “one enzyme-one linkage”
makes enzymatic approaches, especially glycosyltransferases, a much
more efficient, more regio/stereoselective, and more feasible route to
produce oligosaccharides in large scale. |
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| With the wide use of glycosyltransferases, attention has shifted to
the combination of glycosyltransferase with other enzymes to produce
more complex carbohydrates or glycoconjugates with biologically
important elements. During the past twenty years, a multi-enzyme
one-pot reaction fashion with only one purification step has becoming
very popular in carbohydrate synthesis since most of the key enzymes
are proved to be active under similar reaction conditions [3-4]. In
addition to enhanced efficiency, problems such as the availability
of high cost sugar nucleotide donors and product inhibition of
glycosyltransferases have also been solved by following the biosynthetic
pathways: The one-pot reaction can be further conjugated to sugar donor recycling system which generates expensive sugar donors from
cheap precursors, realizing large-scale low-cost enzymatic synthesis of
complex carbohydrates. |
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| Another subject to emerge over the past decade is that in vitro
multi-enzyme carbohydrate synthesis is transferred onto solid beads
or into whole cells. Wang provided examples (“superbeads”) wherein
multi-enzymes are immobilized on Ni-nitrilotriacetic acid beads
[5]. This technique enables reusing of the immobilized enzymes
for several rounds and automated synthesis. To go one step further,
many groups illustrated whole engineered bacterial cells expressing
multi-enzymes for the large-scale synthesis of carbohydrates. This
unique biotechnology avoids isolation and purification of the key
enzymes. On this basis, Wang’s “superbug” uses a single Escherichia
coli strain containing all necessary genes for sugar donor regeneration
and oligosaccharide synthesis on one single plasmid, demonstrating a
powerful living synthetic factory [6]. |
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| The above examples testify the progress of carbohydrate synthesis
with the development of organic synthesis, protein purification,
and molecular genetics. Putative candidates for carbohydrateactive
enzymes are adding to the current list with the advances of
bioinformatics. Some exciting applications are emerging in this field,
including synthesis and modification of carbohydrates via metabolic
pathway engineering in organisms ranging from bacteria to zebrafish.
These achievements, together with earlier examples offer a range of
possibilities for the synthesis of biomaterials. In this regard, enzymatic
synthesis of carbohydrates affords great opportunists for chemists
or synthetic biochemists seeking to find new catalysts and molecular
tools. We hope the journal “Organic Chemistry: Current Research”
intrigues and inspires more chemists to achieve this goal. |
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| References |
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- Werz DB, Ranzinger R, Herget S, Adibekian A, von der Lieth CW, et al. (2007) Exploring the structural diversity of mammalian carbohydrates ("glycospace") by statistical databank analysis. ACS Chem Biol 2: 685-691.
- Leloir LF (1971) Two decades of research on the biosynthesis of saccharides. Science 172: 1299-1303.
- Yu H, Chokhawala HA, Huang S, Chen X (2006) One-pot three-enzyme chemoenzymatic approach to the synthesis of sialosides containing natural and non-natural functionalities. Nat Protoc 1: 2485-2492.
- Chen Y, Thon V, Li Y, Yu H, Ding L, et al. (2011) One-pot three-enzyme synthesis of UDP-GlcNAc derivatives. Chem Commun 47: 10815-10817.
- Chen X, Fang J, Zhang J, Liu Z, Shao J, et al. (2001) Sugar nucleotide regeneration beads (superbeads): A versatile tool for the practical synthesis of oligosaccharides. J Am Chem Soc 123: 2081-2082.
- Chen X, Zhang J, Kowal P, Liu Z, Andreana PR, et al. (2001) Transferring a biosynthetic cycle into a productive Escherichia coli strain: Large-scale synthesis of galactosides. J Am Chem Soc 123: 8866-8867.
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