05 Techniques in Protein Biochemistry

Protein Biochemistry Techniques

  • Overview of laboratory techniques related to proteins

  • Importance of understanding techniques even if not directly relevant to biological contexts

Tenecteplase Protein Structure

  • Amino acid sequence of tenecteplase (fibrinolytic agent)

  • Protein contains 527 amino acids with significant cross-linking between cysteine residues

  • Cross-linking can occur between cysteine residues that are close or far apart in sequence

Chapter Outline

Chapter 5 Topics

  1. The Proteome: Functional Representation of the Genome

  2. Protein Purification as the First Step in Understanding Function

  3. Immunological Techniques in Protein Purification and Characterization

  4. Determining Primary Structure to Understand Protein Function

The Proteome and Genomic Representation

  • Diagram comparing proteome, genome, and transcriptome

  • Proteome: all proteins in a cell/organism

  • Genome: DNA representation

  • Transcriptome: RNA representation

Protein Purification Challenges

  • Purification of proteins is complex and can be a scientific career in itself

  • Variability among proteins necessitates extensive trial and error

  • Some proteins, especially membrane proteins, are difficult to purify due to solubility

Purification Testing

  • Assays are required to confirm protein purity

  • Proteins can be purified based on distinct chemical properties

Key Techniques for Protein Measurement

Spectrophotometry

  • Measures light absorption to determine concentration of proteins in a sample

  • Uses light detection to quantify protein levels based on light absorption characteristics

Bradford Assay

  • A reagent (Coomassie G-250) reacts with proteins; darker color indicates higher protein concentration

  • Importance of using a test sample rather than the entire protein solution to avoid damaging proteins

Assays in Protein Activity Measurement

Lactate Dehydrogenase Assay

  • Measures absorbance of NADH produced in enzymatic reactions

  • Activity of protein can be assessed through enzymatic activity ratios

Specific Activity Measurement

  • Specific activity defined as the ratio of enzyme activity to protein concentration

  • Should increase after each purification step

Importance of Assays in Protein Purification

  • Assays are essential to determine the purity and activity of protein samples

Purifying Proteins from Cells

  • Proteins must be extracted from cells via homogenization and centrifugation

Differential Centrifugation

  • Disrupt cells to create a homogenate and use centrifugation to separate components

  • Requires multiple rounds of centrifugation at varying speeds for purity

Chromatography Techniques

Basics

  • Chromatography is used to separate mixtures based on physical properties

  • Initial use for separating pigments; now encompasses many separation techniques

Types of Chromatography

  1. Gel Filtration Chromatography: separates proteins by size through porous beads

  2. Ion Exchange Chromatography: separates proteins by charge - positively charged proteins bind to negatively charged beads

  3. Affinity Chromatography: uses specific interactions between proteins and chemicals to isolate desired proteins.

Salting Out Technique

  • Salting Out: precipitation of proteins by altering salt concentrations to separate different proteins

Dialysis for Purification

  • Dialysis removes small molecules and salts from protein solutions through semi-permeable membranes

High-Pressure Liquid Chromatography (HPLC)

  • Uses fine beads and high pressure for improved separation and resolving power of proteins

Gel Electrophoresis

SDS-PAGE Technique

  • Proteins undergo denaturation and migration through a gel based on mass due to electric current

  • Visualization achieved through staining techniques

Isoelectric Focusing

  • Technique utilizes pH gradients to separate proteins based on their isoelectric point (pI)

Two-Dimensional Gel Electrophoresis

  • Combines isoelectric focusing and SDS-PAGE to resolve mixtures of proteins based on pI and molecular weight

Immunological Techniques Overview

Antibodies in Protein Purification

  • Antibodies generated against specific proteins to identify and characterize proteins

  • Polyclonal Antibodies: mixtures recognizing multiple epitopes

  • Monoclonal Antibodies: identical, recognizing a specific target epitope

Purifying Estradiol Receptor

  • Esteradiol binds tightly to the estrogen receptor; immunological techniques can be used for purification

Ultracentrifugation and Gradient Centrifugation

  • High-speed centrifugation separates proteins based on sedimentation coefficients

Zonal Centrifugation Method

  • Uses density gradients for identifying protein complexes like the estradiol receptor

Protein Detection Techniques

ELISA (Enzyme-Linked ImmunoSorbent Assay)

  • Used to quantify protein abundance via enzyme-linked antibodies

  • Indirect and sandwich ELISA variations explained

Western Blotting

  • Proteins are transferred from an SDS-PAGE gel to a solid medium and detected using specific antibodies

Understanding Protein Primary Structure

Edman Degradation

  • Technique for sequencing proteins by sequentially removing amino acids

Modern Bioinformatics Methods

  • DNA sequencing has mostly replaced traditional methods, enabling comparative analysis of proteins

Applications of Amino Acid Sequence Analysis

  1. Comparing sequences for functional insights

  2. Inferring evolutionary relationships

  3. Identifying motifs indicative of protein families or functions

Concluding Remarks

  • Insights gathered from amino acid sequences are critical for understanding protein functions and roles in disease.