Glycopeptide

{{Main|N-linked glycosylation}}

N-Linked glycans derive their name from the fact that the glycan is attached to an asparagine (Asn, N) residue, and are amongst the most common linkages found in nature. Although the majority of N-linked glycans take the form GlcNAc-β-Asn{{cite journal |author1=Vliegenthart J. F. G. |author2=Casset F. | year = 1998 | title = Novel forms of protein glycosylation | journal = Current Opinion in Structural Biology | volume = 8 | issue = 5| pages = 565–571 | doi=10.1016/s0959-440x(98)80145-0|pmid=9818259 |hdl=1874/5477 |s2cid=9360182 | hdl-access = free }} other less common structural linkages such as GlcNac-α-Asn{{cite journal |author1=Shibata S. |author2=Takeda T. |author3=Natori Y. | year = 1988 | title = The Structure of Nephritogenoside - a Nephritogenic Glycopeptide with Alpha-N-Glycosidic Linkage | url =http://www.jbc.org/content/263/25/12483.abstract | journal = Journal of Biological Chemistry | volume = 263 | issue = 25| pages = 12483–12485 |doi=10.1016/S0021-9258(18)37780-9 |pmid=3410849|doi-access=free }} and Glc-Asn{{cite journal |author1=Wieland F. |author2=Heitzer R. |author3=Schaefer W. | year = 1983 | title = Asparaginylglucose - Novel Type of Carbohydrate Linkage | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 80 | issue = 18| pages = 5470–5474 | doi=10.1073/pnas.80.18.5470|pmid=16593364 |bibcode=1983PNAS...80.5470W|pmc=384279|doi-access=free }} have been observed. In addition to their function in protein folding and cellular attachment, the N-liked glycans of a protein can modulate the protein's function, in some cases acting as an on-off switch.

Image:GlcNac1.gif

{{Main|O-linked glycosylation}}

O-Linked glycans are formed by a linkage between an amino acid hydroxyl side chain (usually from serine or threonine) with the glycan. The majority of O-linked glycans take the form GlcNac-β-Ser/Thr or GalNac-α-Ser/Thr.

Image:GalNacSer.gif

Of the three linkages the least common and least understood are C-linked glycans. The C-linkage refers to the covalent attachment of mannose to a tryptophan residue. An example of a C-linked glycan is α-mannosyl tryptophan.{{cite journal |author1=Debeer T. |author2=Vliegenthart J. F. G. |author3=Loffler A. |author4=Hofsteenge J. | year = 1995 | title = The Hexopyranosyl Residue That Is C-Glycosidically Linked to the Side-Chain of Tryptophan-7 in Human Rnase U-S Is Alpha-Marmopyranose | journal = Biochemistry | volume = 34 | issue = 37| pages = 11785–11789 | doi=10.1021/bi00037a016 | pmid=7547911|hdl=1874/5760 |s2cid=22324479 | hdl-access=free }}{{cite journal | doi = 10.1007/978-4-431-54836-2_67-1 | title=C-Mannosylation: A Modification on Tryptophan in Cellular Proteins | journal=Glycoscience: Biology and Medicine | pages=1–8| year=2014 | last1=Ihara | first1=Yoshito | last2=Inai | first2=Yoko | last3=Ikezaki | first3=Midori | last4=Matsui | first4=In-Sook L. | last5=Manabe | first5=Shino | last6=Ito | first6=Yukishige | isbn=978-4-431-54836-2 | s2cid=82050024 }}

Several methods have been reported in the literature for the synthesis of glycopeptides. Of these methods the most common strategies are listed below.

Within solid phase peptide synthesis (SPPS) there exist two strategies for the synthesis of glycopeptides, linear and convergent assembly. Linear assembly relies on the synthesis of building blocks and then the use of SPPS to attach the building block together. An outline of this approach is illustrated below.

Image:GlycanSPPS.gif

Several methods exist for the synthesis of monosaccharide amino acid building block as illustrated below.

Image:Glycanbb.gif

Provided the monosaccharide amino acid building block is stable to peptide coupling conditions, amine deprotection conditions and resin cleavage. Linear assembly remains a popular strategy for the synthesis of glycopeptides with many examples in the literature.{{cite journal |author1=Li H. G. |author2=Li B. |author3=Song H. J. |author4=Breydo L. |author5=Baskakov I. V. |author6=Wang L. X. | year = 2005 | title = Chemoenzymatic synthesis of HIV-1V3 glycopeptides carrying two N-glycans and effects of glycosylation on the peptide domain | journal = Journal of Organic Chemistry | volume = 70 | issue = 24| pages = 9990–9996 | doi=10.1021/jo051729z|pmid=16292832 }}{{cite journal |author1=Yamamoto N. |author2=Takayanagi Y. |author3=Yoshino A. |author4=Sakakibara T. |author5=Kajihara Y. | year = 2007 | title = An approach for a synthesis of asparagine-linked sialylglycopeptides having intact and homogeneous complex-type undecadisialyloligosaccharides | journal = Chemistry: A European Journal | volume = 13 | issue = 2| pages = 613–625 | doi=10.1002/chem.200600179|pmid=16977655 }}{{cite journal |author1=Shao N. |author2=Xue J. |author3=Guo Z. W. | year = 2003 | title = Chemical synthesis of CD52 glycopeptides containing the acid-labile fucosyl linkage | journal = Journal of Organic Chemistry | volume = 68 | issue = 23| pages = 9003–9011 | doi=10.1021/jo034773s|pmid=14604374 }}

In the convergent assembly strategy a peptide chain and glycan residue are first synthesis separately. Then the glycan is glycosylated onto a specific residue of the peptide chain. This approach is not as popular as the linear strategy due to the poor reaction yields in the glycosylation step.{{cite journal |author1=Gamblin D. P. |author2=Scanlan E. M. |author3=Davis B. G. | year = 2009 | title = Glycoprotein Synthesis: An Update | journal = Chemical Reviews | volume = 109 | issue = 1| pages = 131–163 | doi=10.1021/cr078291i | pmid=19093879}}

Another strategy to produce glycopeptide libraries is using Glyco-SPOT synthesis technique.{{cite journal |last1=Mehta |first1=AY |last2=Veeraiah |first2=RKH |last3=Dutta |first3=S |last4=Goth |first4=CK |last5=Hanes |first5=MS |last6=Gao |first6=C |last7=Stavenhagen |first7=K |last8=Kardish |first8=R |last9=Matsumoto |first9=Y |last10=Heimburg-Molinaro |first10=J |last11=Boyce |first11=M |last12=Pohl |first12=NLB |last13=Cummings |first13=RD |title=Parallel Glyco-SPOT Synthesis of Glycopeptide Libraries. |journal=Cell Chemical Biology |date=29 June 2020 |volume=27 |issue=9 |pages=1207–1219.e9 |doi=10.1016/j.chembiol.2020.06.007 |pmid=32610041|pmc=7556346 }} The technique extends the existing method of SPOT synthesis.{{cite journal |last1=Hilpert |first1=K |last2=Winkler |first2=DF |last3=Hancock |first3=RE |title=Peptide arrays on cellulose support: SPOT synthesis, a time and cost efficient method for synthesis of large numbers of peptides in a parallel and addressable fashion. |journal=Nature Protocols |date=2007 |volume=2 |issue=6 |pages=1333–49 |doi=10.1038/nprot.2007.160 |pmid=17545971|s2cid=32143600 }} In this method, libraries of glycopeptides are produced on a cellulose surface (e.g. filter paper) which acts as the solid phase. The glycopeptides are produced by spotting FMOC protected amino acids allowing the synthesis to be performed at microgram (nanomole) scale using very small amounts of glycoamino acids. The scale of this technique can be an advantage for creating libraries for screening by using less amounts of glycoamino acids per peptide. However to produce larger quantities of glycopeptides traditional resin-based solid phase techniques would be better.

Native chemical ligation (NCL) is a convergent synthetic strategy based on the linear coupling of glycopeptide fragments. This technique makes use of the chemoselective reaction between a N-terminal cysteine residue on one peptide fragment with a thio-ester on the C-terminus of the other peptide fragment{{cite journal |author1=Nilsson B. L. |author2=Soellner M. B. |author3=Raines R. T. | year = 2005 | title = Chemical synthesis of proteins | journal = Annual Review of Biophysics and Biomolecular Structure | volume = 34 | pages = 91–118 | doi=10.1146/annurev.biophys.34.040204.144700 | pmid=15869385 | pmc=2845543}} as illustrated below.

Image:Sulfur1.gif

Unlike standard SPPS (which is limited to 50 amino acid residue) NCL allows the construction of large glycopeptides. However the strategy is limited by the fact that it requires a cysteine residue at N-terminus, an amino acid residue that is rare in nature. However this problem has partly been address by the selective desulfurization of the cysteine residue to an alanine.{{cite journal |author1=Wan Q. |author2=Danishefsky S. J. | year = 2007 | title = Free Radical Based, Specific Desulfurization of Cysteine: A Powerful Advance in the Synthesis of Polypeptides and Glycopolypeptides | journal = Angew. Chem. | volume = 119 | issue = 48| pages = 9408–9412 | doi=10.1002/ange.200704195|pmid=18046687 |bibcode=2007AngCh.119.9408W }}

• Carbohydrate chemistry
• Glycopeptide antibiotic
• Glycosylation
• Peptide synthesis

{{reflist|30em|refs=

{{cite journal |vauthors=Maverakis E, Kim K, Shimoda M, Gershwin M, Patel F, Wilken R, Raychaudhuri S, Ruhaak LR, Lebrilla CB | title = Glycans in the immune system and The Altered Glycan Theory of Autoimmunity | journal = J Autoimmun | volume = 57 | issue = 6 | pages = 1–13 | year = 2015 | pmid = 25578468 | doi = 10.1016/j.jaut.2014.12.002 | pmc=4340844}}

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• {{cite web | author=Emanual Maverakis |display-authors=etal | title=Glycans in the immune system and The Altered Glycan Theory of Autoimmunity | url= http://ac.els-cdn.com/S0896841114001759/1-s2.0-S0896841114001759-main.pdf?_tid=fbc3820c-0881-11e5-b633-00000aacb362&acdnat=1433179187_223619b43246b42b6d0f8c696bf10ac7}}

• {{Commonscatinline|Glycopeptides}}

{{Glycoproteins}}