The Three-dimentionalStructure of Proteins
The Three-dimentional Structure of Proteins
KeyPrinciplesProtein structures are stabilized by non-covalent interactionsandforces.Protein segmentscanadoptregular secondary structuressuch as the alpha helix and the beta conformation.Tertiary structures is determined by amino acid sequenceThe3Dstructuresofproteinscanbedetermined
Key Principles Protein structures are stabilized by non-covalent interactions and forces. Protein segments can adopt regular secondary structures such as the alpha helix and the beta conformation. Tertiary structures is determined by amino acid sequence. The 3D structures of proteins can be determined
The RelationshipbetweenProteinStructure and Functioninprinciple,proteinscanassumeanuncountablenumberofspecialarrangements,orconformationschemicalorstructuralfunctionsrelatetouniquethree-dimensionalstructures
OverviewofProtein StructureProtein Conformationslimitednumberofconformationspredominateunderbiologicalconditionsconformations=thermodynamicallythemoststable,thatis,lowestfreeenergy (G)native = proteins in any functional, foldedconformations
Overview of Protein Structure
A Protein's Conformation Is Stabilized LargelybyWeakInteractionsstability=tendencyofaproteintomaintainanativeconformationunfoldedproteinshavehighconformationalentropychemical interactionsstabilizenativeconformations=strongdisulfide(covalent)bondsareuncommon-weak (noncovalent)interactionsandforcesarenumerous.hydrogenbonds.hydrophobiceffect.ionicinteractions
PackingofHydrophobicAminoAcidsAwayfrom WaterFavors Protein Foldinghydrophobiceffect=predominating weak interactionsolvationlayer=highlystructuredshellofH,Oaroundahydrophobicmolecule-decreaseswhennonpolargroupsclustertogether- decrease causes afavorable increase in net entropyhydrophobicRchainsformahydrophobicproteincore
PolarGroupsContributeHydrogenBondsandlonPairs to ProteinFoldingrepeatingsecondarystructures(αhelicesandβsheets)optimize hydrogen bondinginteractionofoppositelychargedgroups=ionpair=saltbridge-strengthincreasesinanenvironmentoflowerdielectricconstant, -polaraqueoussolvent:~80- nonpolar protein interior: ~ 4
Individual van der Waals InteractionsAreWeak but CombinetoPromote Foldingvan derWaals interactions =dipole-dipole interactions overshortdistancesindividual interactions contribute little tooverall proteinstabilityhighnumberofinteractionscanbesubstantial
Proteins are Linear Polymers of Amino AcidsRPRR2OH,N-CH-HNHN-CHCH-CH-HH,OAminoacid1Aminoacid2DipeptidePeptide formation is the creation of anamide bondbetween the carboxyl group of one amino acid and theaminogroupofanotheraminoacid
Proteins are Linear Polymers of Amino Acids Peptide formation is the creation of an amide bond between the carboxyl group of one amino acid and the amino group of another amino acid
ThepeptidebondisplanarHInapairoflinked aminoacids,sixatoms(Ca,C,ON,H,and Ca)lie inaplane.Side chains are shown as green balls
The peptide bond is planar In a pair of linked amino acids, six atoms (Cα, C, O, N, H, and Cα) lie in a plane. Side chains are shown as green balls