Development of Purification and Modification Strategies of N-Type Glycopeptide and Glycan Moieties

According  to  the  1997IUPAC recommendations,  the  word  glycan  can  be used as a synonym with polysaccharide(composed of many monosaccharide units).Changing  the  suffix-ose  for –an, describes mannansand  glucans derived from mannose and glucose,respectively. In the context of this work, the    word    glycan    will    be    used    exclusively    to    describe N-glycans, oligosaccharides conjugated to  proteins  via  a  β-N-glycosidic  bond  to  an asparagine side chain. In eukaryotes, N-glycosylation only takes place in the consensus sequon Asn-X-Ser/Thr, (where X can be any amino acid except of proline).  AlthoughN-glycansare  ubiquitous  in  nature,one  of  the  biggest constraints  on  glycoscience  is  the  lack  of  commercially  availableand,  well-characterised glycan standards, for both analytical and structural studies. To be able to study structure-activity relationships of N-glycans they mustbecome more available.This work aims to address this fundamental gap and presents a  detailed  account  ofhowN-glycan  oligosaccharides  can  be  made  more accessible  byusing  naturally  occurring  glycoproteins  and  glycopeptides  as starting materials. 

Chapter 1 gives an overview of the most used natural sources for N-glycan preparative purification, release methods and purification strategies. The subsequent chapters will show how the information of the source can be combined with the appropriate release and purification strategies. Chapter 2 provides a detailed account of the materials and methods used to produce the results shown in subsequent chapters. Chapter 3 presents the application of the oxidative chemical release using NaClO of high mannose glycans from Phaseolus lunatus proteins. Chapter 4 Describes the process of isolation of Sialylglycopeptide (SGP) from chicken egg yolks, which is widely used as a source of complex sialylated N-glycans. Emphasis on the characterization of minor species that can be of synthetic interest is presented. Chapter 5 will show briefly how plant N-glycans obtained by enzymatic release from soybean proteins can be used as a substrate for bacterial exo-glycosidases. Chapter 6 will present a general discussion of the trends and applications of N-glycans as biomaterials, special attention will be given to the field of nanomedicine, an emerging area that faces several challenges where N-glycans can have a positive impact.