生物化学英文版课件：Chapter 7 Carbohydrates Glycobiology

Chapter7

Carbohydrates&Glycobiology碳水化合物与糖生物学2012-10-25Carbohydrate,(C-H2O)n=“Carbon+Water”

SourceofenergyStructure(cottonfibers:cellulose)BuildingblocksCellularrecognition糖类主要是多羟基醛或酮类物质CarbohydratesinfoodareimportantsourcesofenergyUplandcottonproducesthemostwidelyusednaturalfibers,cellulose(apolysaccharide)Cellulose:themostabundantorganiccompoundsinthebiosphere1015kg（1000亿吨）ofcelluloseissynthesizedanddegradedonEartheachyearContents

Monosaccharides（单糖）&disaccharides（二糖）Polysaccharides（多糖）Glycoconjugates（复合糖）:

proteoglycans（蛋白聚糖）,glycoproteins（糖蛋白）,glycolipids（糖脂）WorkingwithcarbohydratesRequirementsforYourUnderstanding

CarbohydrateChemistry

Biologicalfunctions(Glycobiology): glycosaminoglycans&proteoglycans; glycoproteins;glycolipids

MethodsforcarryingoutresearchinglycobiologyfieldMonosaccharidesanddisaccharidesMonosaccharidescontaineither:

aldehyde

group(aldoses)

ketonegroup(ketoses)醛糖酮糖典型单糖丙糖己糖戊糖甘油醛（丙醛糖）二羟丙酮（丙酮糖）Twocommonhexoses:

Pentoses:componentsofnucleicacids(presentinDNA)(presentinRNA)2.Monosaccharidescanbeclassifiedaccordingtothenumberofcarbons:单糖和二糖名字末尾缀以“-ose”

triose 3carbonstetrose 4carbonspentose 5carbonshexose 6carbonsheptose 7carbons4.MonosaccharidestereoisomersHowmanystereoisomersdoesanaldohexosecontain?3.Namingstereoisomers（立体异构体的命名）3waystorepresentthetwosteroisomersofglyceraldehydeenantiomer球棍模型费希尔投影式透视式D-醛糖D-核糖D-阿拉伯糖D-木糖D-来苏糖

红色标记的C

为手性碳；距离羰基最远手性C的构型与D-甘油醛相同，称D型异构体；

方框中的糖是自然界中最普通的糖。D-阿洛糖D-阿卓糖D-古洛糖D-艾杜糖D-塔罗糖D-甘露糖D-半乳糖D-葡萄糖KetoseshaveonefewerasymmetriccenterthanaldoseswiththesamenumberofcarbonsNote:D-酮糖二羟丙酮D-赤藓酮糖

红色标记的C

为手性碳；距离羰基最远手性C的构型与D-甘油醛相同，称D

型异构体；方框中的糖是自然界中最普通的糖。D-核酮糖D-木酮糖D-山梨糖D-塔格糖D-阿洛酮糖D-果糖Epimers（差向异构体）:

twosugarsthatdifferonlyintheconfigurationaroundonecarbonatomD-glucoseandtwoofitsepimers5.Formationofhemiacetal（半缩醛）

orhemiketal（半缩酮）

canoccurwithinamonosaccharideAnaldehydeorketonecanreactwithanalcoholina1:1ratiotoyieldahemiacetalorhemiketal,creatinganewchiralcenteratthecarbonylcarbon.

呋喃糖吡喃糖OnlyaldoseshavingfiveormorecarbonatomscanformpyranoseringsmutarotationAnomers:differintheirconfigurationabouteitherhemiacetalorhemiketalcarbonatomAnomers(twocyclicformsofD-glucose)CreateanasymmetricCenter（异头物碳原子）C-1:anomericcarbonatom变旋光[a]D25°C=+112°[a]D25°C=-19°旋光性Opticalrotation

异头物六元环的吡喃醛糖比五元环的呋喃酮糖稳定变旋现象（mutarotation)异头物（anomer）的形成D-葡萄糖C-1的醛基与C-5的羰基反应形成半缩醛，具有两种立体异构体，a和b异头物。a和b异头物之间的相互转化的过程称为变旋现象。Definitionofspecificrotation[a]D25°C[a]D25°C=observedopticalrotation(°)Opticalpathlength(dm)xconcentration(g/mL)Theopticalactivity

（光活性）isexpressedquantitativelybyitsopticalrotation（旋光性）:

Levorotatoryisomer(-):rotatesplane-polarizedlighttotheleft

（左旋异构体）(counterclockwise);Dextrorotatoryisomer(+):rotatesplane-polarizedlighttotheright

（右旋异构体）(clockwise)当平面偏振光通过手性化合物溶液后，偏振面的方向就被旋转了一个角度。这种能使偏振面旋转的性能称为旋光性。手性化合物都具有旋光性。

hemiacetalacetalaldehyde醛半缩醛缩醛麦芽糖

Twomonosaccharidesareconnectedthroughglycosidic

linkagetoformdisaccharides.

O-glycosidicbondSubstitutionofasecondalcoholmoleculeproducesanacetalorketal.ReducingendEnexampleofD-glucosemutarotation(Pleaserefer:problemNo.4ofChapter7)Theequilibriummixtureconsistsof64%β-D-glucopyranoseand36%α-D-glucopyranose.Itcontainstraceamountoftheopen-chainform.Mutarotation变旋现象Mutarotation变旋现象Mutarotationisthechangeinspecificrotationthataccompaniestheinter-conversionof

and

-anomersinaqueoussolution.

Mutarotationiscommontoallcarbohydratesthatexistinhemiacetalforms,anditwasoneofthephenomenathatsuggestedthataldosesmightexistascyclichemiacetals.Mutarotationoccurswhenpureanomersaredissolvedinaqueoussolution.Analdehydecannotundergomutarotation.Haworthperspectiveformulas（Haworth透视式）:commonlyusedtoshowthestereochemistryofringformsofmonosaccharides(SirWaterN.Haworthwon1937NobelPrizeinChemistry)呋喃吡喃吡喃葡萄糖呋喃果糖ConformationofpyranoseringsThechairformismorestablebecauseoflesssterichindranceastheaxialpositionsareoccupiedbyhydrogenatoms.b-D-glucopyranose

sterichindrance(predominatedform)AxisEquatorialposition吡喃糖的构象形式空间障碍轴赤道椅式船式6.Reactionsofmonosaccharides单糖具有还原性amixtureofproducts（reducing3molofCu2+permoleofglucose）Applicationtodiagnosisofdiabetesmellitus(determinationofglucoseconcentration)Fehling’sreaction

费林反应

(notspecific!)Moresensitivemethod:using

glucoseoxidase(onlyspecificforglucose)NonenzymaticreactionofglucosewithaprimaryaminogroupinhemoglobinAmadorirearrangementcyclizationglycationendproductsThenonenzymaticreactionofglucosewithaprimaryaminogroupinhemoglobin:formationofaSchiffbase;(2)undergoestheAmadorirearrangementtogenerateastableproduct;(3)thisketoaminecanfurthercyclizetoyieldGHB;(4)Subsequentreactionsgenerateadvancedglycationendproducts(AGEs),suchasε-N-carboxymethyllysineandmethylglyoxal,compounds(5)AGEs

damageotherproteinsbycross-linkingthem,causingpathologicalchanges.7.Monosaccharidederivativesaldonicaciduronicacid糖醛酸醛糖酸葡萄糖醛酸葡萄糖酸葡糖胺胞壁酸半乳糖胺甘露糖胺脱氧糖类鼠李糖墨角藻糖N-乙酰神经氨酸（唾液酸）8.Formationofdisaccharides

Twomonosaccharidesareconnectedthroughglycosidic

linkage

（糖苷键）toformdisaccharides.O-glycosidicbondreducingend二糖的形成Somecommondisaccharides

Nonreducingsugar!Containsnofreeanomericcarbonatomnonreducingdisaccharidesarenamedasglycosides乳糖蔗糖海藻糖Somerulestonameoligosaccharides

Givetheconfigurationattheanomericcarbonjoiningthefirstmonosaccharideunittothesecond.Namethenonreducingreside;todistinguishfive-andsix-memberedringstructures,insert“furano”or“pyrano”intothename.Indicateusingtheparenthesesthetwocarbonatomsjoinedbytheglycosidicbond,withanarrowconnectingthetwonumbers.Namethesecondresidue.Ifthereisathirdresidue,describethesecondglycosidicbondbythesameconventions.Adouble-headedarrowisusedfornonreducingdisaccharide(glycosides).Sucrose:Glc(

12

)FruExample:maltoseconventionalname:-D-glucopyranosyl-(14)-D-glucopyranosesimplifiedname:

Glc(14)GlcPolysaccharides(glycans)

Ashighas2x107DaltonsStorageformsofglucose

starch(plant)amylose(un-branched)amylopection(branched)

glycogen(animals)Structuralroles

Cellulose(eg.cotton)Chitin(Arthropods,节肢动物)Glycosaminoglycans(animals)多糖Differencesbetweenhomopolysaccharidesandheteropolysaccharides同多糖杂多糖2.HomopolysaccharidesStarch(amylose直链淀粉,amylopectin支链淀粉

)

unbranchedpolymerofD-glucose-a(1,4)-D-glucose

branchedpolymerofD-glucose-a(1,4)-D-glucosewitha

(1,6)branchpointAclusterofamyloseandamylopectin(instarchgranules)strandsofamylopectinformdouble-helicalstructureswitheachotherorwithamylosestrands

Glucoseresiduesatthenonreducingendsareremovedenzymaticallyduringmobilizationofstarchforenergyproduction.3.SomehomopolysaccharidesservestructuralrolesCellulose

unbranchedpolymerofD-glucose-b(1,4)-D-glucosetheb

configurationallowscellulosetoformverylongandstraightchain.scaledrawingofsegmentsoftwoparallelcellulosechain

3.SomehomopolysaccharidesservestructuralrolesChitin几丁质

unbranchedpolymerofD-N-acetylglucosamine-b(1,4)-D-N-acetylglucosamine由b(1,4）糖苷键连接N-乙酰-D-葡糖胺而形成的同多糖4.StericfactorsandhydrogenbondinginfluencehomopolysaccharidefoldingThefoldingofpolysaccharidesinthreedimensionsfollowsthesameprinciplesasthosegoverningpolypeptidestructure:

hydrogenbondhydrophobicinteractionsvanderWaalsinteractionselectrostaticinteractionsThethree-dimensionalstructuresaredescribedintermsofdihedralangles,analogoustoanglesmadebythepeptidebond.AmapoffavoredconformationsforoligosaachridesandpolysaccharidesRelativeenergyDisaccharideGal(β1→3)GalSimilarto:Ramachandranplot(tovisualizedihedralanglesψagainstφofaminoacidresiduesinproteinstructure.Thestructureofstarch(amylose)CoiledhelicalstructureMoststableconformationiscurved,ratherthanlinearThehydroxylgroupshavebeenomitted.CellulosebreakdownbywoodfungiAwoodfungusgrowingonanoaklog（橡树）.Allwoodfungihavetheenzymecellulase,whichbreaksthe(β1→4)glycosidicbondsincellulose,sothatwoodisasourceofmetabolizablesugar(glucose)forthefungus.Theonlyvertebratesabletousecelluloseasfoodarecattleandotherruminants(sheep,goats,camels,giraffes).Theextrastomachcompartment(rumen)ofaruminantteemswithbacteriaandprotiststhatsecretecellulase.Fromthestructuresofcelluloseandstarch(glycogen),welearn:Thedifferentconsequencesofthe

aandblinkages

havebiologicalsignificance.Thestraightchainformedby

b

linkagesisoptimalfortheconstructionoffibershavingahightensilestrength.Theopenhelixformedbyalinkagesiswellsuitedtoformanaccessiblestoreofsugars.Mammalslackcellulasesthatthereforecannotdigestwoodandvegetablefibers.Whynotstoreglucoseinitsmonomericform?

Ithasbeencalculatedthathepatocytesstoreglycogenequivalentto[glucose]=0.4M;theactual[glycogen]=0.01mM.Ifincytosol[glucose]=0.4M,leadingtoosmoticentryofwaterthatmightrupturethecell.Ifintracellular[glucose]=0.4M,comparedwithextracellular(inbloodofamammal)[glucose]=5mM,thefree-energychangeforglucoseuptakeintocellswouldbeprohibited.Epimers（差向异构体）:

twosugarsthatdifferonlyintheconfigurationaroundonecarbonatomD-glucoseandtwoofitsepimersEpimerizationThecarbonatomatwhichtheinitialdeprotonationtakesplaceisastereocenter.If,forexample,D-Glucose(anAldose)rearrangestoD-Fructose,theketose,thestereochemicalconfigurationislostintheenolform.Inthechemicalreactiontheenolcanbeprotonatedfromtwofaces,resultinginthebackformationofglucoseortheformationoftheepimerD-mannose.Lobry-deBruyn-vanEkensteintransformation

Itisthebaseoracidcatalyzedtransformationofanaldoseintotheketoseisomerorviceversa,withatautomeric(互变异构的)enediolasreactionintermediate.Ontheoriginofelementaryhexoses(HirabayashiJ.)

(1)Formalreaction,anautocatalyticpolymerizationreaction,occurredontheprimitiveearthunderweaklyalkalineconditionstogeneratevarioussmallmolecularcompounds.(2)Amongthem,glyceraldehydeanddihydroxyacetoneundergoaldolcondensationtoproducestableketohexoses,fructoseandsorbose（山梨糖）.(3)Subsequently,LobrydeBruynrearrangementconvertsfructoseintostablealdohexoses,glucose,andmannose.QRevBiol.1996Sep;71(3):365-80.(4)Thus,prebioticallysynthesized“firsttriplet”hexoseswouldhavebeenavailableforutilizationbyancestralprimitivemicroorganisms.(5)Afterthedevelopmentofbiochemicalpathways,varioussaccharides,includinggalactose,werebiosynthesizedfromglucoseandmannoseas“bricolageproducts”;theutilizationofgalactoseasakeyrecognitionmolecule,basedonitsdistinctiveaxial4-OHanditsoutermostlocationinglycoconjugates,owingtoitslatearrival,mayhaveevolvedconcomitantlywiththeevolutionofmulticellularorganisms.(bora)(bora)Mutarotationalsooccursonoligosaccharidesandpolysaccharides!But,forpolysaccharides,itisnotdetectable!5.GlycosaminoglycansareheteropolysaccharidesoftheextracellularmatrixAtleastoneofsugarsintherepeatingunithasanegativelychargedcarboxylateorsulfategroup透明质酸硫酸软骨素硫酸角质素肝素糖胺聚糖糖醛酸N-乙酰葡糖胺艾杜糖醛酸

半乳糖

细胞外介质：杂多糖+纤维蛋白（胶原蛋白、弹性蛋白）成纤维细胞1.Hyaluronate(透明质酸):存在于眼球玻璃体、关节液和皮肤等组织中作为润滑剂和撞击缓冲剂，并有助于阻滞入侵的微生物及毒性物质的扩散。

2.Chondroitin4-sulfate(硫酸软骨素):动物组织的基础物质，用以保持组织的水分和弹性。包括软骨素Ａ、Ｂ、Ｃ等数种，软骨素Ａ是软骨的主成分。和肝素相似，可用以降血脂，改善动脉样硬化症状。此外，硫酸软骨素还有消除皱纹、使皮肤保持及富弹性的作用。硫酸软骨素主要存在于鸡皮、鱼翅、鲑鱼头和鸡等软骨内。3.Haparin(肝素):高度硫酸酯化的右旋多糖，与蛋白质结合大量存在于肝脏之中，其他器官和血液中也有。肝素有强的抗凝血作用，临床上用肝素钠盐预防或治疗血栓的形成，肝素也有消除血液脂肪的作用。

Themoleculesarecopolymersofalternatinguronicacidandaminosugarresidues(keratansulfateistheexception),withsulfateestersinanyofseveralpositions,exceptinhyaluronan.Theionizedcarboxylateandsulfategroupsgivethesepolymerstheircharacteristichighnegativecharge.Therapeuticheparincontainsprimarilyiduronicacid(IdoA)andasmallerproportionofglucuronicacid(GlcA),andisgenerallyhighlysulfatedandheterogeneousinlength.葡萄糖醛酸艾杜糖醛酸

Space-fillingmodelshowsaheparinsegmentIdoAOSproteins:fibroblastgrowthfactor(FGF1)FGFR(R:receptor)ligand:heparinTheirinteraction:

electrostaticinteractionHeparinisshowninaball-and-stickrepresentation,withthenegativecharges(—SO3–and—COO–)attractedtothepositive(blue)surfaceoftheFGF1protein.Heparinwasusedinthisexperiment,buttheglycosaminoglycanthatbindsFGF1invivoisheparansulfateonthecellsurface.

InteractionbetweenaglycosaminoglycananditsbindingproteinGlycoconjugates:proteoglycans,

蛋白聚糖glycoproteins（糖蛋白）

&glycolipids（糖脂）Proteoglycans:macromoleculesofthecellsurfaceorextracellularmatrixinwhichoneormore

glycosaminoglycanchainsarejoined covalentlytoamembraneproteinora secretedproteinGlycoproteins:proteinscovalentlyattachedbyoneorseveral oligosaccharidesGlycolipids:membranelipidsinwhichthehydrophilichead groupsareoligosaccharides.复合糖1.Proteoglycans:glycosaminoglycan-containing macromolecules(glycosaminoglycan)(linker)Functionaslubricantsandstructuralcomponentsinconnectivetissue,mediateadhesionofcellstotheextracellularmatrixandbindfactorsthatstimulatecellproliferation蛋白聚糖：糖胺聚糖

+蛋白蛋白聚糖theassociationbetweencellsandtheproteoglycanofextra-cellularmatrixismediatedbyamembraneprotein(integrin)andbyanextracellularprotein(fibronectin)withbindingsitesforbothintegrinandtheproteoglycan.Cell–matrixinteractions

anchorcellstoextracellularmatrixdirectthemigrationofcellsindevelopingtissueconveyinformationinbothdirectionsacrossplasmamembrane(viaintegrins)纤连蛋白整合素肌动蛋白丝（微丝）

Proteoglycansformaggregatesattheextracellularmatrix

Proteoglycanaggregatescaninteractwithcollagenintheextracellularmatrixofcartilage,contributingtothedevelopmentandtensilestrengthoftheconnectivetissue.

Proteoglycansresemblepolysaccharidesmorethanproteinsasmuchasthecarbohydratemakesupasmuchas95%ofthebiomoleculebyweight透明质酸分子结构Electronmicrographofaproteoglycan（蛋白聚糖）

aggregatepurifiedfromcalfcartilageRosemanS(2001)ReflectionsonglycobiologyJ.Biol.Chem.276,41,527-542Oneverylongmoleculeofhyaluronanisassociatednoncovalentlywithabout100moleculesofthecoreproteinaggrecan.Eachaggrecanmoleculecontainsmanycovalentlyboundchondroitinsulfateandkeratansulfatechains.Linkproteinsatthejunctionbetweeneachcoreproteinandthehyaluronanbackbonemediatethecoreprotein–hyaluronaninteraction.

膜蛋白聚糖（membraneproteoglycans）

Syndecansareheldinthemembranebyhydrophobicinteractionsbetweenasequenceofnonpolaraminoacidresiduesandplasmamembranelipids;

Sydecanscanbereleasedbyasingleproteolyticcutnearthemembranesurface.Inatypicalsyndecan,theextracellularaminoterminaldomainiscovalentlyattached(bytetrasaccharidelinkers)tothreeheparansulfatechainsandtwochondroitinsulfatechains.

MembraneProteoglycan:glypicanCurrentOpinioninStructuralBiology2012,22:583-590Syndecanscooperatewithintegrinstoregulatecelladhension

Glypicansareheldinthemembranebyacovalentlyattachedmembranelipid(GPIanchor),andareshedifthelipid-proteinbondiscleavedbyaphospholipase.All

glypicans

have14conservedCysresidues,whichformdisulfidebondstostabilizetheproteinmoiety,andeithertwoorthreeglycosaminoglycanchainsattachednearthecarboxylterminus,closetothemembranesurface.MembraneProteoglycan:GlypicanDeficiencyinglypican-3(GCP3)gene,whichencodesaheparansulfateproteoglycan(HSPG，硫酸乙酰肝素类蛋白聚糖

),resultedinSimpson-Golabi-Behmelsyndrome;Thissyndromeischaracterizedbyawidevarietyofclinicalmanifestationsincludingpre-natalandpost-natalovergrowthsyndrome,phenotypicallysimilartoBeckwith-Wiedemannsyndrome(贝-威综合征).贝-威综合征(常染色体显性遗传):以巨大舌，脐膨出和生长过剩为三大主要特征的先天性疾病，同时伴有内脏肿大（主要为肝、肾和脾的肿大），出生时低血糖，单侧肥大（身体的一侧生长过剩）等生长异常。Reference:Simpson-Golabi-BehmelSyndromeassociatedwithrenaldysplasiaandembryonaltumor:LocalizationofthegenetoXqcen-q21.Hughes-BenzieRM,HunterAGW,AllansonJE,MackenzieAE.Am.J.Med.Genet1992;43:428-435Dr.

DavidReidoftheDepartmentofChemistryattheUniversityofCambridge,revealedthatthestudyhasshownthatthecharacteristictoughnessandstiffnessofboneispredominantlyduetothepresenceofspecializedsugars,notproteins.Theyobservedthatsugars,particularlyproteoglycansandglycosaminoglycans,appearedtoplayarolewhichisasimportantasproteinsincontrollingbonemineralization,theprocessbywhichnewly-formedboneishardenedwithmineralssuchascalciumphosphate.Newfindingsontreatmentsforosteoporosis(骨质疏松)OneoftheNSdomainsisshowninmoredetail,revealingahighdensityofmodifiedresidues:GlcNS(N-sulfoglucosamine),withasulfateesteratC-6;andbothGlcAandIdoA,withasulfateesteratC-2.TheexactpatternofsulfationintheNSdomaindiffersamongproteoglycans.NAdomain:N-acetylateddomainNSdomain:SulfateddomainFourtypesofproteininteractionswithNSdomainsofheparansulfate抗凝血酶：antithrombinFGF:

成纤维细胞生长因子

2.Glycoproteinsareinformation-richcontainingoligosaccharidesglycosidicbondN-glycosylbond糖蛋白：富含信息Whatarethebiologicaladvantagesofaddingoligosaccharidestoproteins?

alterthepolarityandsolubilityoftheirconjugatedproteinsinfluenceprotein-foldingeventsprotectsomeproteinsfromattackby

proteolytic

enzymescomplexofoligosaccharidesisenormouslyrichin

structuralinformationsomeproteinspresenttissueglycoforms

(mayactasatissue-specificmark)3.Glycolipids（糖脂）andlipopolysaccharides

（脂多糖）aremembranecomponentsGangliosides:神经节苷脂

membraneglycolipidsofeukaryoticcellsinwhichthepolarheadgroupformstheoutersurfaceofthemembraneExample:theoligosaccharidemoietiesofthegangliosidesdeterminehumanbloodgroupsLipopolysaccharides(LPS,脂多糖，endotoxin,

细菌内毒素):dominantsurfacefeatureoftheoutermembraneofgram-negativebacteria.-targetofantibody-toxictohumans-inflammationstimulator(炎症刺激物)

Theprincipaldeterminantoftheserotype(immunologicalreactivity)ofthebacterium4.Oligosaccharide-lectininteractionsmediatemanybiologicalprocessesLectin（凝集素

）:

proteinsthatbindcarbohydrateswithhighaffinity

(hydrogen-bonding)andspecificity(lectinscanbeeasilydistinguishedbytheirbindingwithvarioussimilarsugars).involvedinawidevarietyofcell-cellrecognitionandadhesionprocessesLectinmicroarraytechnology–analysisofglycansCurrentopinioninChemistryBiology2009,13:427-432Selectins:选择蛋白afamilyoflectins,foundinplasmamembranes,thatmediatecell-cellrecognitionandadhesion.Roleoflectin-ligandinteractionsinlymphocytemovementtothesiteofaninfectionorinjury游离的淋巴细胞AneutrophilcirculatingthroughacapillaryisslowedbytransientinteractionsbetweenP-selectinmoleculesintheplasmamembraneofthecapillaryendothelialcellsandglycoproteinligandsforP-selectinontheneutrophilsurface.AsitinteractswithsuccessiveP-selectinmolecules,theneutrophilrollsalongthecapillarysurface.Nearasiteofinflammation,strongerinteractionsbetweenintegrininthecapillarysurfaceanditsligandintheneutrophilsurfaceleadtotightadhesion.Theneutrophilstopsrollingand,undertheinfluenceofsignalssentoutfromthesiteofinflammation,beginsextravasation—escapethroughthecapillarywall—asitmovestowardthesiteofinflammation.HelicobacterpyloricellsadheringtothegastricsurfacecausesulcersbyinteractionsbetweenabacterialsurfacelectinandtheLeboligosaccharide(abloodgroupantigen)ofthegastricepithelium导致胃炎和胃溃疡的细菌:幽门螺杆菌(Helicobacterpylori)TheNobelPrizeinPhysiologyorMedicine2005两位科学家于1982年的发现幽门螺杆菌，使得原本慢性的、经常无药可救的胃溃疡变成了只需抗生素和一些其他药物短期就可治愈的疾病。

Alectin-carbohydrateinteractionBovinemannose6-phosphatereceptorcomplexedwithmannose6-phosphate.Mannose6-phosphateishydrogen-bondedtoArg111andcoordinatedwiththemanganeseion.Eachhydroxylgroupofmannoseishydrogen-bondedtotheprotein.TheHis105hydrogen-bondedtoaphosphateoxygenofmannose6-phosphatemaybetheresiduethat,whenprotonatedatlowpH,causesthereceptortoreleasemannose6-phosphateintothelysosome.HydrophobicinteractionsofsugarresiduesSugarunitssuchasgalactosehaveamorepolarsidethatisavailabletohydrogen-bondwiththelectin,andalesspolarsidethatcanhavehydrophobicinteractionswithnonpolarsidechainsintheprotein,suchastheindoleringofTrpresidues.proteinlectinsugarRolesofoligosaccharidesinrecognitionandadhesionatthecellsurface

Oligosaccharideswithuniquestructures,componentsofavarietyofglycoproteinsorglycolipidson