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SEPARATION AND DETECTION OF PROTEINS Part I Vlasta Němcová, Michael Jelínek, Jan Šrámek
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detection directly in the cells - fluorescent staining detection following isolation and separation of proteins - SDS-PAGE (sodium dodecylsulfate polyacrylamide gel electrophoresis) Identification of actin, microfilamentum structure of the cell cytoskeleton by 2 methods:
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METHOD 1: Fluorescent staining of F-actin, G-actin and DNA F-actin: phalloidin conjugated with TRITC G-actin: DNase I conjugated with Alexa Fluor 488 DNA: DAPI cells used – cell line NES2Y (human -cells of Langerhans islets)
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Fixation – first step of sample preparation preserve the tissue from decay, either through autolysis or putrefaction purpose - to preserve the biological material (tissue or cells) as close to its natural state as possible in the process of preparing samples for examination Formaldehyde creats covalent chemical bonds between proteins in tissue anchors soluble proteins to the cytoskeleton tissue becomes more rigid (easier manipulation)
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Protocol: fixation of the cells using solution of formaldehyde in PBS (phosphate buffered saline) removal of formaldehyde solution from the cells by repeated wash with PBS incubation with phalloidin-TRITC and DNase I- Alexa Fluor 488 removal of unbound phalloidin-TRITC and DNase I-Alexa Fluor 488 by repeated wash with PBS staining with DAPI observation under fluorescent microscope
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METHOD 2: Comparison of actin and myosin expression in different types of tissues - by SDS-PAGE (sodium dodecylsulfate polyacrylamide gel electrophoresis) Isolation of proteins from different tissues: tissues used: muscle heart liver
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Isolation of proteins from cells and tissues: chemical (we use in our experiment) mechanical physical first step – desintegration of the tissue and cells desintegration (=lysis) of cells
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Isolation of proteins transfer of a tissue sample into a tube desintegration of the tissue by a lysis buffer containing SDS (sodium dodecylsultate) separation of the lysate containing proteins from tissue fragments by centrifugation by the Bradford method using BSA (bovine serum albumine) as a standard for calibration curve construction Determination of protein concentration Protocol:
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Separation of proteins by the SDS-PAGE method boiling of the samples with sample buffer containing SDS loading the samples containing desired amount of protein onto a polyacrylamide gel separation of proteins by vertical gel electrophoresis Identification of actin and myosin staining of the gel with the separated proteins in Coomassie blue solution detection of localization of actin and other proteins in SDS-PAGE, comparison of actin and myosin expression among tissues
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Determination of protein concentration: several methods are routinely used all of the listed methods rely on the use of a spectrophotometer (measurement of absorbance) the Bradford assay (we use in our experiment) Lowry assay BCA assay (Bicinchoninic assay) ultraviolet absorbance assay, etc.
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Principle of the Bradford method colorimetric assay based on absorbance shift of Bradford reagent that occurs after its binding to proteins Bradford reagent contains Coomassie Brilliant Blue G-250 dye that binds to basic and aromatic amino acid residues (arginine (ARG), fenylalanin (PHE), tryptophan (TRY) a prolin (PRO)
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Coomassie Brilliant Blue G-250 when the dye binds to proteins, it is converted to blue color the amount of this blue form is detected at 595 nm to quantify the concentration of proteins
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Calibration curve
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preparation of standards for construction of a calibration curve – several samples with known concentration of protein (bovine serum albumine = BSA dissolved in water is routinely used) dilution of our sample (lysate) with unknown concentration to fit into the concentration range of the calibration curve incubation of standards and our samples with Bradford reagent absorbance measurement (A595) construction of a calibration curve determination of protein concentration in the lysate using the calibration curve Bradford assay
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The Lowry assay based on detection of tyrosine and tryptophan residues blue color is developed and detectable with a spectrophotometer in the range of 500-750 nm Another methods for protein determination:
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Ultraviolet absorbance assay determination of protein concentration by ultraviolet absorption (260 to 280 nm) depends on the presence of aromatic amino acids in proteins (tyrosine and tryptophan) [ Protein] (mg/mL) = 1.55*A 280 - 0.76*A 260
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BCA method BCA = bicinchoninic acid the peptide bond itself is responsible for color development purple color is detectable at 562 nm
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