英文蛋白质结构课堂练习

BiochemistryProteinGProteinGisamultidomainextracellularproteinfoundinseveralStreptococcalspecies.The"proteinG"referredtointhisquizisactuallyonlytheB1domainofoneoftheseproteins.TheserepeateddomainsbindtotheFcportionofIgG.ThereisnostructuralsimilaritybetweenthesedomainsandtheStrepAprotein,whichhassimilarbindingproperties.StructureofProteinG

(frontviewandsideview)1.

proteinGaminoterminus?2.

proteinGcarboxylterminus?StructureofProteinG

(backview)3.

-hairpinmotif?(2)4.

atypeI(or"common")turn?WhichistypeIturnthatconnects-strandsatthecarboxyl-terminusStructureofProteinG(sideview)5.

hydrophilicsurfaceofthe

-helix?6.

positiveendofan

-helicaldipole?7.

hydrophobicsurfaceon

-strands?StructureofProteinG1.AportionoftheproteinG-sheetisshownwithouttheside-chainsandwiththebackbonedisplayedasSticks.Hydrogenbondsareindicatedasdashedlinesbetweenthe

-strands.

NotethattheH-bondsontheleftareperpendiculartothechaindirection,whereasthoseontherightaremoreevenly-spaced,butaresetatanangletothechaindirection.

TheH-bondsbetweentheparallel–strands?StructureofProteinG2.Asegmentoftheα-helixbackboneisshownasSticks.TheGlu27residueisshownasBallandStickandtheotherside-chainsareWireframe.ClickontheatomthatdonatesahydrogenbondtothebackboneC=OofGlu27.StructureofProteinG3.ThreeresiduesneartheN-terminusofproteinGareshownasBallandStick:Phe52,Thr53,andVal54.ThepeptidebondbetweenThr53andVal54?StructureofProteinG4.Threeresiduesinthe-helixofproteinGareshownasBallandStick:Ala24,Thr25,andAla26.Helicalgeometryisfixedbypreferreddihedralanglesaboutthesetwobackbonebonds:

(Psi),rotationabouttheC-Csinglebond;and

(Phi),rotationabouttheN-Csinglebond.The

or

bondoftheThr25residue?StructureofProteinG5.ThedisplayisSpacefillwithStructurecoloringexceptthatthe-helixbackboneisshownasBallandStick(withamagentaspiraltracingthehelix).ThelocationofThr25neartheN-terminusofthehelixislabelled.Pickanα-helicalresidueabout10ÅfromThr25.StructureofProteinG6.Asegmentofthe-helixbackboneisshownasSticks.TheGlu27residueisshownasBallandStickandtheotherside-chainsareWireframe.ClickontheatomthatacceptsahydrogenbondfromtheN-HofLys28.StructureofProteinG7.ThedisplayisSpacefillwithStructurecoloringexceptthatthreestrandsofthe

-sheetareshownasSticks.OnestrandisshownasBallandStickwithThr2neartheN-terminuslabeled.Pickaresidueonthesame

-strandas,andabout15ÅfromThr2.StructureofProteinG1.TheC-terminal

-hairpinstructureisshownwiththesidechainsoffivethreoninesdisplayedasBallandStick.Distances(inÅunits)betweenthreepairsoftheseresiduesareshownasdashedredlines.PickthemostlikelyofthesepotentialH-bondsthatalsooccursbetweenresiduesonthesame-strand.StructureofProteinG2.Thesidechainsonthesolvent-exposedsurfaceofthe

-sheetareshownasBallandStick.TheremainderofproteinGisWireframewithStructurecoloring.Mostofthesidechainsherearepolar.Inaddition,twoarebasic.Pickoneofthesebasicsidechains.StructureofProteinG3.ThebackboneisshownasStickswithStructurecoloring.Thesidechainsofthearomaticresidues(Tyr,Trp,andPhe)aredisplayedasBallandStickandcoloredCPK.ClickontheresiduethatisresponsibleformostoftheUVabsorbanceat280nm.StructureofProteinG4.Thesidechainsonthehydrophilicsurfaceofthe-sheetareshownasSpacefill.Asnotedinapreviousquestion,nearlyallofthesesidechainsarepolar.Infact,Ile6istheonlyapolarsidechainonthesolvent-exposedsurfaceofthe-sheet.ClickonIle6.StructureofProteinG5.ThesidechainsofthesixaromaticresiduesareshownasSpacefill.Thissideviewshowshowtheyfillthehydrophobiccorebetweenthe

-helixand

-sheetofproteinG.PickaPheresidue.StructureofProteinG6.ThesequenceofproteinGisshownusingtheone-letteraminoacidcode.ThesegmentscorrespondingtosecondarystructuresareindicatedwithRasMolStructurecoloring.Fromthegroupsoffiveaminoacidslistedbelowthesequence,pickthegroupthatisnotfoundinproteinG.StructureofProteinG