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PROTEINS

FOLDEDPOLYPEPTIDES

©2007PaulBillietODWSPRIMARYSTRUCTUREThesequenceofaminoacidsMIL1sequence:>gi|7662506|ref|NP_056182.1|MIL1protein[Homosapiens]MEDCLAHLGEKVSQELKEPLHKALQMLLSQPVTYQAFRECTLETTVHASGWNKILVPLVLLRQMLLELTRLGQEPLSALLQFGVTYLEDYSAEYIIQQGGWGTVFSLESEEEEYPGITAEDSNDIYILPSDNSGQVSPPESPTVTTSWQSESLPVSLSASQSWHTESLPVSLGPESWQQIAMDPEEVKSLDSNGAGEKSENNSSNSDIVHVEKEEVPEGMEEAAVASVVLPARELQEALPEAPAPLLPHITATSLLGTREPDTEVITVEKSSPATSLFVELDEEEVKAATTEPTEVEEVVPALEPTETLLSEKEINAREESLVEELSPASEKKPVPPSEGKSRLSPAGEMKPMPLSEGKSILLFGGAAAVAILAVAIGVALALRKKlength:386aminoacids©Anne-MarieTernes

PRIMARYSTRUCTUREThenumbersofaminoacidsvary

(e.g.insulin51,lysozyme129,haemoglobin574,gammaglobulin1250)TheprimarystructuredeterminesthefoldingofthepolypeptidetogiveafunctionalproteinPolaraminoacids(acidic,basicandneutral)arehydrophilicandtendtobeplacedontheoutsideoftheprotein.Non-polar(hydrophobic)aminoacidstendtobeplacedontheinsideoftheprotein©2007PaulBillietODWSInfinitevarietyThenumberofpossiblesequencesisinfinite

Anaverageproteinhas300aminoacids,

Ateachpositiontherecouldbeoneof20differentaminoacids

=10390possiblecombinationsMostareuseless

Naturalselectionpicksoutthebest©2007PaulBillietODWSSECONDARYSTRUCTURE

ThefoldingoftheN-C-Cbackboneofthepolypeptidechainusingweakhydrogenbonds

©ScienceStudent©Text2007PaulBillietODWSSECONDARYSTRUCTUREThisproducesthealphahelixandbetapleatingThelengthofthehelixorpleatisdeterminedbycertainaminoacidsthatwillnotparticipateinthesestructures

(line)©DrGaryKaiser

©Text2007PaulBillietODWSTERTIARYSTRUCTURE

ThefoldingofthepolypeptideintodomainswhosechemicalpropertiesaredeterminedbytheaminoacidsinthechainMIL1protein©Anne-MarieTernes

©2007PaulBillietODWSTERTIARYSTRUCTUREThisfoldingissometimesheldtogetherbystrongcovalentbonds

(e.g.cysteine-cysteinedisulphidebridge)Bendingofthechaintakesplaceatcertainaminoacids

(line)HydrophobicaminoacidstendtoarrangethemselvesinsidethemoleculeHydrophilicaminoacidsarrangethemselvesontheoutside©2007PaulBillietODWS©MaxPlanckInstituteforMolecularGeneticsChainBofProteinKinaseCQUATERNARYSTRUCTURESomeproteinsaremadeofseveralpolypeptidesubunits

(e.g.haemoglobinhasfour)ProteinKinaseC©MaxPlanckInstituteforMolecularGenetics©Text2007PaulBillietODWSQUATERNARYSTRUCTUREThesesubunitsfittogethertoformthefunctionalproteinTherefore,thesequenceoftheaminoacidsintheprimarystructurewillinfluencetheprotein'sstructureattwo,threeormorelevels©2007PaulBillietODWSResult

ProteinstructuredependsupontheaminoacidsequenceThis,inturn,dependsuponthesequenceofbasesinthegene

©2007PaulBillietODWSPROTEINFUNCTIONS

ProteinstructuredeterminesproteinfunctionDenaturationorinhibitionwhichmaychangeproteinstructurewillchangeitsfunctionCoenzymesandcofactorsingeneralmayenhancetheprotein'sstructure©2007PaulBillietODWSFibrousproteinsInvolvedinstructure:tendonsligamentsbloodclots

(e.g.collagenandkeratin)Contractileproteinsinmovement:muscle,microtubules

(cytoskelton,mitoticspindle,cilia,flagella)©2007PaulBillietODWSGlobularproteins

mostproteinswhichmovearound(e.g.albumen,caseininmilk)Proteinswithbindingsites:

enzymes,haemoglobin,immunoglobulins,membranereceptorsites©2007PaulBillietODWSProteinsclassifiedbyfunction

CATALYTIC:enzymesSTORAGE:ovalbumen(ineggs),casein(inmilk),zein(inmaize)TRANSPORT:haemoglobinCOMMUNICATION:hormones(eginsulin)andneurotransmittersCONTRACTILE:actin,myo