Protein purification and Analysis Why purify proteins Pure

Why purify proteins? • Pure proteins are required to study enzyme function • Pure

Steps in protein purification • Develop assay • Choose source of protein • Prepare

Differential Centrifugation transfer supernatant 1000 g tissue homogenate 10, 000 g Pellet unbroken cells

Affinity Chromatography Add excess ligand

SDS poly acrylamide electrophoresis (PAGE) SDS = H 3 C-(CH 2)11 -CH 2 -OSO

Isoelectric Focusing p. H 3 Decreasing p. H - Decreasing p. H 9 +

2 -D Electrophoresis - - Decreasing MW Decreasing p. H SDS-PAGE + + Decreasing

Amino Acid Analysis 1) Acid hydrolyze protein 2) Treat with phenylisothiocyanate (PICT) + 3)

Protein Sequencing (Edman Degradation) 1) Repeat 2) Trifluoroacetic acid 3) + Can sequence in

Generate Proteolytic Fragments Endopeptidases • Typsin • Chymotrypsin cleaves at COOH end of Lys

Peptide mapping exercise Met-Ala-Arg- Gly-Glu-Tyr-Met-Cys-Lys-Phe-Ala-Glu-Gln-Asp Trypsin Met-Ala-Arg Phe-Ala-Glu-Gln-Asp Gly-Glu-Tyr-Met-Cys-Lys Chymotrysin Met-Ala-Arg- Gly-Glu-Tyr Met-Cys-Lys –Phe

Slides: 15

Download presentation

Protein purification and Analysis

Why purify proteins? • Pure proteins are required to study enzyme function • Pure proteins are required for structural analysis (x-ray crystallography, NMR spectroscopy) • Pure proteins are required to obtain amino acid sequence

Steps in protein purification • Develop assay • Choose source of protein • Prepare tissue extract – cell disruption – subcellular fractionation • Protein fractionation (several steps) • Determination of purity

Differential Centrifugation transfer supernatant 1000 g tissue homogenate 10, 000 g Pellet unbroken cells nuclei chloroplast transfer supernatant 100, 000 g Pellet mitochondria Pellet microsomal Fraction (ER, golgi, lysosomes, peroxisomes) Super. Cytosol, Soluble enzymes

Chromatography

Gel Permeation Chromatography

Affinity Chromatography Add excess ligand

SDS poly acrylamide electrophoresis (PAGE) SDS = H 3 C-(CH 2)11 -CH 2 -OSO 3 SDS – denatures protein coats w/ negative charge --- -- --- Used to determine protein MW And purity of protein prep

Isoelectric Focusing p. H 3 Decreasing p. H - Decreasing p. H 9 + +

2 -D Electrophoresis - - Decreasing MW Decreasing p. H SDS-PAGE + + Decreasing p. H

Amino Acid Analysis 1) Acid hydrolyze protein 2) Treat with phenylisothiocyanate (PICT) + 3) Separate derivatized AA’s by HPLC

Protein Sequencing (Edman Degradation) 1) Repeat 2) Trifluoroacetic acid 3) + Can sequence in 30 to 60 AA’s from N-terminus

Generate Proteolytic Fragments Endopeptidases • Typsin • Chymotrypsin cleaves at COOH end of Lys and Arg cleaves at COOH end of Phe, Tyr, Trp Chemical Cleavages • Cyanogen Bromide cleaves at COOH end of Met Generate overlapping fragments Sequence individual fragements and piece together sequence

Peptide mapping exercise Met-Ala-Arg- Gly-Glu-Tyr-Met-Cys-Lys-Phe-Ala-Glu-Gln-Asp Trypsin Met-Ala-Arg Phe-Ala-Glu-Gln-Asp Gly-Glu-Tyr-Met-Cys-Lys Chymotrysin Met-Ala-Arg- Gly-Glu-Tyr Met-Cys-Lys –Phe Ala-Glu-Gln-Asp CNBr Met-Ala-Arg- Gly-Glu-Tyr Met-Cys-Lys -Phe-Ala-Glu-Gln-Asp