扬州大学：《生物化学 Biochemistry》课程教学课件（PPT讲稿）5 Protein Function

Protein Function

Protein Function

KeyPrinciplesThe functions of many proteins involve the reversible binding ofothermolecules (ligands).A ligand binds a protein at a binding site that is complementary tothe ligand in size, charge, and hydrophobic or hydrophiliccharacter.ProteinsareflexibleThe binding of a protein and a ligand is often coupled to aconformational change intheproteinthatmakes the binding sitemore complementary to the ligand, permitting tighter bindingInamulti-subunit protein,a conformational change in onesubunit oftenaffectstheconformationofothersubunits

Key Principles  The functions of many proteins involve the reversible binding of other molecules (ligands).  A ligand binds a protein at a binding site that is complementary to the ligand in size, charge, and hydrophobic or hydrophilic character.  Proteins are flexible.  The binding of a protein and a ligand is often coupled to a conformational change in the protein that makes the binding site more complementary to the ligand, permitting tighter binding.  In a multi-subunit protein, a conformational change in one subunit often affects the conformation of other subunits

Proteins Function by InteractingDynamicallywithOtherMoleculestwotypesofinteractions:-proteinactingasareactioncatalyst,orenzyme,altersthe chemical configurationorcompositionof a boundmoleculeneitherthechemical configurationnorthecompositionoftheboundmoleculeischanged

Reversible Binding of a Protein to a ligandoxygen-binding proteinsOxygen Can Bind toa HemeProstheticGroupoxygen:-poorlysolubleinaqueoussolutions-diffusionthroughtissues is ineffectiveoverlargedistances-transitionmetalshavestrongtendencytobind(iron,copper)

Reversible Binding of a Protein to a ligand: oxygen-binding proteins

HemeProstheticGroupheme=protein-boundprostheticgrouppresentinmyoglobin andhemoglobin-consistsofacomplex organicCHringstructure,(a)(b)Hprotoporphyrin,Nelsoins&Cox Lehninisty, 8e, 0 2021 W:Hcnceowitha boundFe2+atom

Coordination Bonds of Ironsixcoordinationbonds- four to nitrogen atoms in the flat porphyrin ringtwoperpendiculartotheporphyrintozo(b)CH(c)

GlobinsAreaFamilyofOxygen-BindingProteinsglobins=widespreadproteinfamilyCarboxyltermi-highlyconservedtertiary structure:HicsHisF8eight a-helicalsegmentsconnectedbyAminoterminusbends (globinfold)一mostfunctioninO2transportorstorage

Types of Globinsfourtypesinhumansandothermammals-myoglobin=monomeric,facilitatesO,diffusioninmuscletissuehemoglobin=tetrameric,responsibleforO2transportinthebloodstreamneuroglobin=monomeric,expressedlargelyinneuronstoprotectthebrainfromlowO2orrestrictedbloodsupplycytoglobin=monomeric,regulateslevelsofnitricoxide,alocalizedsignalformusclerelaxation

MyoglobinHas a Single Binding SiteforOxygenmyoglobin:153residues+onemoleculeofheme-bendsnamedaftertheα-helicalsegmentstheyconnectHis93=ninety-thirdresidefromtheaminoterminalendHisF8=eighthresidueinahelixF

Protein-Ligand Interactions CanBeDescribedQuantitivelyasimpleequilibriumexpressiondescribesthereversible binding of aprotein (P)toa ligand (L)P + L= PLNochemistry

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