Nat. Commun.: recognition of sugar sequence by combinatorial method

Protein and DNA sequencing have revolutionized modern biology, and are even very popular among non scientists However, it is surprising that conventional high-throughput sequencing techniques cannot be used for oligosaccharides Due to the lack of tools for carbohydrate structure sequencing, the development of glycosyl chemistry has been slow, which has become an important obstacle This is also due to the unique complexity of its natural biopolymers The basic concept of tandem mass spectrometry (MS) analysis of (biological) polymer sequences depends on two basic assumptions: the molecular structure of the fragment product must be translatable to the parent polymer by retaining the structural characteristics of the precursor; and there must be available effective measures to provide sufficient level of fragment structure details to retrieve the structure of the precursor First of all, these prerequisites are protein and nucleic acid, which are linear biopolymers formed by their non isomeric monomers The parent sequence can be deduced only from M / Z data The situation of sugars is more complicated, because most of the monomers are isomers or chiral isomers of each other, so it is necessary to identify the regional and stereochemical data of the glycosidic bond In addition, the structural characteristics of these isomers are not easy to be solved by traditional MS technology So far, little is known about the structural characteristics of these sugars preserved during fragmentation Due to these limitations, the interpretation of the unknown structure of oligosaccharides from biological sources is mainly dependent on NMR, which may mean several months of extraction and purification work to obtain enough samples, and may also change the unstable functional groups during this period IR fingerprints of various monosaccharides and disaccharides (source: Nat Commun.) a team led by Isabelle Compagnon from the University of Lyon reported a combination approach that allowed them to sequence sugars by combining IR with MS In mass spectrometer, sugar compounds are broken down into monosaccharide fragments Then IR is used to further analyze the IR spectra of those fragments The researchers first used the method to analyze disaccharides They showed that the IR fingerprint region of a specific type of monosaccharide fragment (so-called C fragment) can be used to identify monosaccharide content and identify stereochemical information about glycosidic bonds between sugars The spectral analysis of disaccharides (source: Nat Commun.) in the traditional IR spectrum, the 3 μ m spectral range has little molecular specificity due to the interference of aqueous solvent However, this spectral range is highly specific for carbohydrate compounds in gas phase Now, this highly correlated spectral analysis method has been extended to non derived carbohydrate compounds Several diagnostic fingerprints of monosaccharide isomers have been reported, including hexose, hexuronic acid, n-acetylhexosamine, sulfated and phosphorylated monosaccharides Recently, the research team also reported the spectral identification of oligosaccharide isomers The researchers now further promote the 3 μ m fingerprint as a method to solve the problem of isomerism identification of sugar compounds IR fingerprint can also be used to identify the stereochemical structure of glycoside bond However, two limitations of this sugar analysis method can be expected First, the identification of oligosaccharides will depend on the availability of the corresponding standards Secondly, the resolution of MS / IR fingerprint decreased with the increase of oligosaccharide size In order to overcome these two limitations, top-down sequencing must be used IR spectra integrated into MS provide the possibility of spectral analysis via building blocks after MS / MS fragmentation It is found that the monosaccharide content and stereochemical structure of oligosaccharides can be elucidated by spectral analysis of monosaccharide segments Therefore, we can use the monosaccharide content and the step-by-step spectral analysis of stereochemistry to distinguish the carbohydrate sequence After that, the team applied the sequencing method to longer oligosaccharides Compared with other MS based sequencing strategies, the proposed method has three advantages First of all, it does not need any chemical derivatization of the analyte, which saves a lot of sample preparation Second, the minimum database of monosaccharide standards is sufficient for spectral identification of monosaccharide content and stereochemistry of any oligosaccharide Finally, the advantage of MS sequencing strategy is combined with the high resolution of IR spectrum to the isomers of saccharides This method can be used independently or complementarily with other sequencing strategies Nicolas C parfer, of the University of Florida, said: "the key point of this study is that even if the glycosidic bond is cut, the chirality of the glycosidic bond will not change This observation has an important impact on carbohydrate sequencing, because the glycosidic bond is usually the most unstable bond in larger sugars." 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