A protease is an enzyme that catalyzes the hydrolysis of the...

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A protease is an enzyme that catalyzes the hydrolysis of thepeptide bo...

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A segment of the main chain of the protease could hydrogen bondto the main chain of the substrate to form an extended parallel orantiparallel pair of strands Proteasomes S elective protein degradationoccurs in the proteasome a large protein complex located in thenucleus and cytosol of eukaryotic cells The proteasome core complex which has asedimentation coefficient of 20S contains 2copies each of 14 different polypeptides 7 atype proteins form each of the two a rings at the ends ofthe cylindrical structure 7 btype proteins form each of the two central b rings The 20S proteasome core complex encloses a cavity consisting of 3 compartments joined bynarrow passageways See diagrams p 1360 1362 Protease activities are associated with threeof the b subunits each having different substratespecificity One catalytic b subunit has a chymotrypsinlike activity with preference fortyrosine or phenylalanine at the P1 peptide cabonylposition One has a trypsinlike activity withpreference for arginine or lysine at the P1 position One has a postglutamyl activity withpreference for glutamate or other acidic residue at the P1position Different variants of the three catalyticsubunits with different substrate specificity are produced incells of the immune system that cleave proteinsfor antigen display The proteasome hydrolases constitute a unique family of threonine proteases A conserved Nterminalthreonine is involved in catalysis at each active site The threecatalytic b subunits are synthesized as preproteins They areactivated when the Nterminus is cleaved off making threonine theNterminal residue Catalytic threonines are exposed at the lumenalsurface Proteasomaldegradation ....

A protease is an enzyme that catalyzes the hydrolysis of the peptide bonds of target proteins....

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