Lecture20

Lecture20 - ecture 20 11/18/11 Background reading: Berg, et...

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Unformatted text preview: ecture 20 11/18/11 Background reading: Berg, et al: Pages 65 - 79 Garrett and Grisham: Pages 148 - 152 Outline: Serine proteases The proteome Protein purification Protein extraction Protein isolation Analyses of results Use of recombinant DNA technology in protein purification Serine proteases Chymotrypsin is a member of a family of proteases that utilize the same catalytic strategy as we described in the last lecture in which a catalytic triad helps to generate a powerful nucleophile (serine) which enables the formation of a covalent tetrahedral intermediate hich is stabilized by interactions with peptide NH groups in a region known as the oxyanion hole. Trypsin is another member of this family and its amino acid sequence has about 40% homology to the sequence of chymotrypsin. The similarity in structure between these two proteases is shown in the overlay of the ribbon models of these structures at the left. (Red = chymotrypsin). Both enzymes use the same catalytic mechanism but differ in substrate specificity. This specificity difference is reflected by the presence of different R groups in the specificity pockets. For example an aspartate is located in the pocket of trypsin. Some other proteases have been found to use the same catalytic mechanism as chymotrypsin but have apparently arisen by divergent evolution. In general, enzymes adopt conformations that are structurally and chemically complementary to the transition states of the reactions that they catalyze. The proteome The availability of the entire genomic DNA sequences of a wide variety of organisms has provided us an extremely valuable resource for use in protein biochemistry. It must be remembered that these genomes are simply inventories of the genes that might be expressed in a particular tissue at a particular time....
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Lecture20 - ecture 20 11/18/11 Background reading: Berg, et...

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