《糖生物学》课程教学课件（讲稿）10 glycobiology concept and oligosaccharide conformation（2）

1. Concept of Glycobiology

1.#Concept#of#Glycobiology

Learning object: The classes of glycoconjugates and theirlocations in eukaryoticcells: The type of function served by glycosylation

Learning#object# • The#classes#of#glycoconjugates#and#their# loca;ons#in#eukaryo;c#cells# • The#type#of#func;on#served#by#glycosyla;on#

. The challenge of glycobiology is to define thebiologicalfunctions of sugars attached to proteinsandmembranesandtodeterminehowthesefunctions are carried out.: Although this challenge is ongoing, the principlesthat describe how protein- and lipid- linked sugarsmediate biological processes are becoming clear.· The goal of this lectureisto illustrate thethemesthat underlie the functions of glycoproteins andglycolipids by highlighting well-understood examplesof how the carbohydrate portions of these moleculeswork

• The#challenge#of#glycobiology#is#to#define#the# biological#func;ons#of#sugars#a?ached#to#proteins# and#membranes#and#to#determine#how#these# func;ons#are#carried#out.## • Although#this#challenge#is#ongoing,#the#principles# that#describe#how#proteinD#and#lipidD#linked#sugars# mediate#biological#processes#are#becoming#clear.# • The#goal#of#this#lecture#is#to#illustrate#the#themes# that#underlie#the#func;ons#of#glycoproteins#and# glycolipids#by#highligh;ng#wellDunderstood#examples# of#how#the#carbohydrate#por;ons#of#these#molecules# work.#

1.1 The field of glycobiologyencompasses the multiple functions ofsugars attached to proteins and lipids

1.1 The field of glycobiology encompasses the multiple functions of sugars attached to proteins and lipids

EnergymetabolismincellsPathwaytoabstract energyfrom breakdownofglucoseandglycogenGlycogen is even linked to protein coreThe function of sugar molecules as forms of energy for storageand transport isgenerally considered to fall outsidethefield ofglycobiology

Energy#metabolism#in#cells# Pathway#to#abstract#energy#from#breakdown#of# glucose#and#glycogen# Glycogen#is#even#linked#to#protein#core# The$func)on$of$sugar$molecules$as$forms$of$energy$for$storage$ and$transport$is$generally$considered$to$fall$outside$the$field$of$ glycobiology.$

Glycoconjugates: mono-, oligo-, or polysaccharides areattachedtoproteins orlipidsGenerallycomplexheteropolymers,ratherthanrepeating homopolymers, such as glycogen and amyloseThe sugars of glycoproteins and glycolipids are referredas GlycansNo singlepredominantfunctionof protein-and lipid-linkedglycans.Similartoproteins,which servediversefunctionsasenzymes,hormones,transportersand structural elements

Glycoconjugates:#monoD,#oligoD,#or#polysaccharides#are# a?ached#to#proteins#or#lipids# Generally#complex#heteropolymers,#rather#than# repea;ng#homopolymers,#such#as#glycogen#and#amylose# The#sugars#of#glycoproteins#and#glycolipids#are#referred# as#Glycans No$single$predominant$func)on$of$protein:$and$lipid:linked$ glycans.$ Similar$to$proteins,$which$serve$diverse$func)ons$as$enzymes,$ hormones,$transporters$and$structural$elements.$

Physical propertiesProviding structural componentsofglycansCell wallsExtracellularmatrixIntrinsicfunctionsperformed by glycansModifying protein propertiesSolubilityProteinsandlipidsareStabilityscaffoldsDirecting trafficking of glycoconjugatesAffect the intrinsic propertiesIntracellularof proteinsExtracellularExtrinsicfunctionsMediating and modulating cell adhesionresultingfromCell-cell interactionsglycan-lectin interactionsCell-matrix interactionsMediating and modulating signallingIntracellularExtracellularTaylorand DrickamerIntroduction toGlycobiology

Physical$proper)es$$ of$glycans Proteins$and$lipids$are$$ scaffolds$ Affect$the$intrinsic$proper)es$$ of$proteins$

1.2 There are three major classes ofglycoconjugates

1.2 There are three major classes of glycoconjugates

Serumand otherfluidsThose attached to lipidsThose attached to proteinsLuminalcompartmentsthrough N (N-linked)O-linked glycanNucleusCPlasmaMembraneCytoplasmReflectsthehistoricalavailability of serumglycoproteinsExtracellularmatrixLuminal/extraceliularglycansCytopiasmic/nuclearAn integral partof the secretoryglycansProteinmachinery of the cellRLipid

Those attached to lipids Those attached to proteins through N (N-linked) O-linked glycan Reflects the historical availability of serum glycoproteins An integral part of the secretory machinery of the cell

Electron micrographofendothelial cells from a blood capillaryCourtesyofGeorgeE.Palade(NP1974)VascularlumendecoratedwithparticlesofcationizedferritinEssentials of GlycobiologyICBChapter 1, Figure 4Second Edition

Chapter#1,#Figure##4# Electron micrograph of endothelial cells from a blood capillary Essen%als(of(Glycobiology(( Second#Edi;on Courtesy of George E. Palade (NP 1974) decorated with particles of cationized ferritin