Comprehensive Study Notes on Protein Separation Techniques and Antibodies

Class Overview

  • Last class covered methods related to protein separation and analysis.

Methods of Protein Separation

  • Two Types of Separation:

    • Native PAGE (Polyacrylamide Gel Electrophoresis)

    • SDS-PAGE (Sodium Dodecyl Sulfate PAGE)

Native PAGE

  • Proteins are separated based on their size and charge without denaturing.

  • Uses their natural structure via:

    • Adding SDS (Sodium Dodecyl Sulfate)

    • Boiling and reducing agents

  • Comparison of protein size and charge:

    • Same size proteins can be separated based on charge only.

    • Charges vary due to amino acid composition (e.g., presence of glycine vs. tryptophan).

Isoelectric Focusing (IEF)

  • Definition: A method to separate proteins based on their charge at specific pH levels.

    • Isoelectric Point (pI): The pH at which a protein’s net charge is zero.

  • The proteins migrate toward their pI in a pH gradient.

    • Example gradient: from pH 4 to pH 10.

  • At their pI, proteins stop moving in the electric field.

Practical Application of IEF

  • Visual representation of proteins on a strip:

    • Proteins situated based on their own charge at their respective pI.

  • Explanation of two-dimensional (2D) gel electrophoresis:

    • Involves separating proteins first by charge (IEF) and then by molecular weight (SDS-PAGE).

Protocol for 2D Gel Electrophoresis:

  1. Load proteins in a strip with an existing pH gradient.

  2. Apply electric current to facilitate movement towards their pI.

  3. After the first dimension, treat the proteins with SDS.

  4. Separate proteins based on size in the second dimension (SDS-PAGE).

Observations and Challenges

  • A complex pattern emerges in 2D gels where:

    • Proteins of the same size may have different acidic/basic properties, affecting behavior.

    • Need for comparison of control vs cancer cells to understand presence or absence of specific proteins.

Identification of Proteins of Interest

  • Use of Antibodies: Essential for identifying specific proteins within gel samples.

    • Structure of antibodies:

    • Consists of heavy and light chains with antigen-binding sites.

  • Properties of antibodies:

    • Specificity: Ability to recognize the exact target protein only.

    • Sensitivity: Detection limits for small quantities of proteins.

    • Affinity: Strength of binding to the target protein.

Distinguishing Between Terms

  • Specific: Recognizes only a specific target.

  • Sensitive: Detects low amounts of substance.

  • Affinity: Refers to binding strength to the target.

Immunology Brief

  • Introduction to generating antibodies for research:

    • Use the target protein as an antigen for immune response generation.

    • Inject the antigen (protein) into a rabbit for antibody development.

    • Collect and purify antibodies from serum derived from the immune response.

Antigen vs. Antibody

  • Antigen: Any foreign substance that induces the immune response and produces antibodies (e.g., proteins).

    • Derivation: "Anti" means against, and "gen" means generate.

  • B-cells:

    • Part of the adaptive immune system, produce antibodies, activated by binding antigens.

    • Memory B-cells retain information for future responses to the same antigen.

Antibody Production Types

  • Polyclonal Antibodies:

    • Derived from multiple B-cell clones, bind to multiple epitopes on the same antigen.

    • Example application: detecting various forms of a protein in assays.

Monoclonal Antibodies:

  • Definition: Antibodies produced from a single clone of B-cells targeting a specific epitope.

  • Hybridoma Technique: Method to produce monoclonal antibodies:

    1. Immunize a mouse to produce B-cells targeting a specific antigen.

    2. Fuse these B-cells with myeloma (tumor) cells to create hybridoma.

    3. Select and clone hybridomas that produce the desired antibody.

    4. Result: A stable source of monoclonal antibodies with specificity for one epitope.

Summary of Antibody Use in Research

  • Antibodies can be incorporated into detection methods alongside electrophoresis techniques.

  • Monitoring protein presence or quantifying levels in various experimental setups.

Conclusion

  • Understanding the complex methods of protein separation, identification through antibodies, and their implications in research and diagnostics is vital for cell biology.