Antibodies


 Title Antibody

 
Antibodies [also called immunoglobulins (Igs)] are multi-component glycoproteins which recognize and bind antigens (substances recognized by the immune system which induce an immune reaction). They are integral to immune system function and human health. However, since their discovery around the end of the 19th century, they first emerged as an incredibly powerful tool for research applications, and more recently as potent facilitators of new therapeutic approaches.

 

 Antibody

The Binding  Site 

     

Antibody-antigen affinity is mediated by conformational complementarity with hypervariable (HV) regions found within the variable domains of both light and heavy chains. Antigen binding involves various non-covalent interactions, including van der Waals, electrostatic, and hydrophobic forces. HV region sequencing differs extensively between molecules, creating antibody specificity.

The

Hinge


IgA, IgD, and IgG possess a flexible string of amino acids in the central part of each heavy chain, termed the "hinge" region, where they are linked to each other through disulfide bonds. This provides conformational plasticity, allowing for the creation of different antigen-antibody complexes. IgE and IgM lack this hinge, but still demonstrate flexibility.

Heavy Chains


Antibodies consist of four polypeptide chain subunits, two of which are identical “heavy” chains. Each heavy chain has a “variable” domain, which facilitates antigen binding, and multiple “constant” domains, which define heavy chain isotype (μ, δ, γ, α, or ε).

Light Chains


The other two polypeptide chain subunits of an antibody are identical ~25 kDa “light” chains typically tethered to heavy chains. Antibodies can contain either λ or κ light chains (but never both) regardless of heavy chain isotype. Like heavy chains, light chains also contain variable and constant domains, but only possess one of each per chain.

 
 

Isotypes


Antibodies are classified into IgA, IgD, IgE, IgG, and IgM isotypes corresponding to heavy chain isotypes α, δ, ε, γ, and μ, respectively. IgA and IgG can be further divided into subclasses (2 for IgA, 4 for IgG). These isotypes differ in their structures, distributions, and functions. Several Ig subtypes also form oligomers. The different subtypes of Ig are: momomer, dimer, and pentamer.

 

 Isotype 2x

 

Distributions: serum, mucosal areas (secretory)
Function: prevent mucosal pathogen colonization 
Whole molecule size: ~160 kDa (monomer)
Heavy chain size: ~55 kDa
Structure: monomer, dimer/tetramer
 


 

    

 
Distribution: B-cell
Function: B-cell activation
Whole molecule size: ~180 kDa 
Heavy chain size: ~60 kDa
Structure: monomer
 


 

    

 
Distribution: B cells (monomer), serum (pentamer) 
Function: anti-pathogen early-response
Whole molecule size: ~970 kDa
Heavy chain size: ~70 kDa
Structure: monomer, pentamer
 


 

    

 
Distribution: Mast Cells
Function: allergic response; anti-parasite 
Whole molecule size: ~190 kDa
Heavy chain size: ~70 kDa
Structure: monomer
 


    

 

 
Distribution: serum
Function: antibody-based immunity 
Whole molecule size: ~150 kDa
Heavy chain size: ~50 kDa
Structure: monomer
 

 




Fab and FC Regions


Antibodies have three distinct parts: two antibody binding regions (Fab) and one constant region (Fc). Fab regions facilitate antigen-antibody interactions while Fc regions bind to endogenous Fc receptors on immune cells. Enzyme cleavage with pepsin generates a F(ab)’2 fragment with significant degradation of the F(c). In contrast, enzymatic cleavage with papain digests the immunoglobulin molecule into F(ab) and F(c) fragments. 
Fab Regions  



Primary Antibodies



These are antibodies raised against a specific antigen of interest and are typically unconjugated (unlabelled) but for some applications can be conjugated too. The antigen could be any type of biomolecule: protein, peptide, carbohydrate, or other small molecule. A good primary antibody recognizes and binds with high affinity and specificity a unique epitope. A primary antibody can be very useful for the detection of biomarkers. This is for high importance in the diagnostics of diseases such as cancer, diabetes, Parkinson’s and Alzheimer’s disease.




Primary Button
 

Secondary Antibodies



Secondary antibodies bind to the primary antibody to assist in detection, sorting and purification of target antigens. To enable detection, the secondary antibody must have specificity for the antibody species and isotype of the primary antibody being used and generally is conjugated.
 

Secondary Button

 

 



Antibodies have become one of the most important tools for studying protein function in cells. The specificity of the antibody-antigen reaction, combined with the ability to link one or the other to fluorescent tags, enzymes, or other markers, makes antibodies versatile tools in both basic and clinical research.

                    

 

                        Check out our selection of Primary and Secondary Antibodies!