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
No chemistry