Epitope

Last updated

An epitope, also known as antigenic determinant, is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. The part of an antibody that binds to the epitope is called a paratope. Although epitopes are usually non-self proteins, sequences derived from the host that can be recognized (as in the case of autoimmune diseases) are also epitopes. [1]

Contents

The epitopes of protein antigens are divided into two categories, conformational epitopes and linear epitopes, based on their structure and interaction with the paratope. [2] Conformational and linear epitopes interact with the paratope based on the 3-D conformation adopted by the epitope, which is determined by the surface features of the involved epitope residues and the shape or tertiary structure of other segments of the antigen. A conformational epitope is formed by the 3-D conformation adopted by the interaction of discontiguous amino acid residues. In contrast, a linear epitope is formed by the 3-D conformation adopted by the interaction of contiguous amino acid residues. A linear epitope is not determined solely by the primary structure of the involved amino acids. Residues that flank such amino acid residues, as well as more distant amino acid residues of the antigen affect the ability of the primary structure residues to adopt the epitope's 3-D conformation. [3] [4] [5] [6] [7] 90% of epitopes are conformational. [8]

Function

T cell epitopes

T cell epitopes [9] are presented on the surface of an antigen-presenting cell, where they are bound to major histocompatibility complex (MHC) molecules. In humans, professional antigen-presenting cells are specialized to present MHC class II peptides, whereas most nucleated somatic cells present MHC class I peptides. T cell epitopes presented by MHC class I molecules are typically peptides between 8 and 11 amino acids in length, whereas MHC class II molecules present longer peptides, 13–17 amino acids in length, [10] and non-classical MHC molecules also present non-peptidic epitopes such as glycolipids.

B cell epitopes

The part of the antigen that immunoglobulin or antibodies bind to is called a B-cell epitope. [11] B cell epitopes can be divided into two groups: conformational or linear. [11] B cell epitopes are mainly conformational. [12] [13] There are additional epitope types when the quaternary structure is considered. [13] Epitopes that are masked when protein subunits aggregate are called cryptotopes. [13] Neotopes are epitopes that are only recognized while in a specific quaternary structure and the residues of the epitope can span multiple protein subunits. [13] Neotopes are not recognized once the subunits dissociate. [13]

Cross-activity

Epitopes are sometimes cross-reactive. This property is exploited by the immune system in regulation by anti-idiotypic antibodies (originally proposed by Nobel laureate Niels Kaj Jerne). If an antibody binds to an antigen's epitope, the paratope could become the epitope for another antibody that will then bind to it. If this second antibody is of IgM class, its binding can upregulate the immune response; if the second antibody is of IgG class, its binding can downregulate the immune response.[ citation needed ]

Epitope mapping

T cell epitopes

MHC class I and II epitopes can be reliably predicted by computational means alone, [14] although not all in-silico T cell epitope prediction algorithms are equivalent in their accuracy. [15] There are two main methods of predicting peptide-MHC binding: data-driven and structure-based. [11] Structure based methods model the peptide-MHC structure and require great computational power. [11] Data-driven methods have higher predictive performance than structure-based methods. [11] Data-driven methods predict peptide-MHC binding based on peptide sequences that bind MHC molecules. [11] By identifying T-cell epitopes, scientists can track, phenotype, and stimulate T-cells. [16] [17]

B cell epitopes

There are two main methods of epitope mapping: either structural or functional studies. [18] Methods for structurally mapping epitopes include X-ray crystallography, nuclear magnetic resonance, and electron microscopy. [18] X-ray crystallography of Ag-Ab complexes is considered an accurate way to structurally map epitopes. [18] Nuclear magnetic resonance can be used to map epitopes by using data about the Ag-Ab complex. [18] This method does not require crystal formation but can only work on small peptides and proteins. [18] Electron microscopy is a low-resolution method that can localize epitopes on larger antigens like virus particles. [18]

Methods for functionally mapping epitopes often use binding assays such as western blot, dot blot, and/or ELISA to determine antibody binding. [18] Competition methods look to determine if two monoclonal antibodies (mABs) can bind to an antigen at the same time or compete with each other to bind at the same site. [18] Another technique involves high-throughput mutagenesis, an epitope mapping strategy developed to improve rapid mapping of conformational epitopes on structurally complex proteins. [19] Mutagenesis uses randomly/site-directed mutations at individual residues to map epitopes. [18] B-cell epitope mapping can be used for the development of antibody therapeutics, peptide-based vaccines, and immunodiagnostic tools. [18] [20]  

Epitope tags

Epitopes are often used in proteomics and the study of other gene products. Using recombinant DNA techniques genetic sequences coding for epitopes that are recognized by common antibodies can be fused to the gene. Following synthesis, the resulting epitope tag allows the antibody to find the protein or other gene product enabling lab techniques for localisation, purification, and further molecular characterization. Common epitopes used for this purpose are Myc-tag, HA-tag, FLAG-tag, GST-tag, 6xHis, [21] V5-tag and OLLAS. [22] Peptides can also be bound by proteins that form covalent bonds to the peptide, allowing irreversible immobilisation. [23] These strategies have also been successfully applied to the development of "epitope-focused" vaccine design. [24] [25]

Epitope-based vaccines

The first epitope-based vaccine was developed in 1985 by Jacob et al. [26] Epitope-based vaccines stimulate humoral and cellular immune responses using isolated B-cell or T-cell epitopes. [26] [20] [17] These vaccines can use multiple epitopes to increase their efficacy. [26] To find epitopes to use for the vaccine, in silico mapping is often used. [26] Once candidate epitopes are found, the constructs are engineered and tested for vaccine efficiency. [26] While epitope-based vaccines are generally safe, one possible side effect is cytokine storms. [26]  

Neoantigenic determinant

A neoantigenic determinant is an epitope on a neoantigen, which is a newly formed antigen that has not been previously recognized by the immune system. [27] Neoantigens are often associated with tumor antigens and are found in oncogenic cells. [28] Neoantigens and, by extension, neoantigenic determinants can be formed when a protein undergoes further modification within a biochemical pathway such as glycosylation, phosphorylation or proteolysis. This, by altering the structure of the protein, can produce new epitopes that are called neoantigenic determinants as they give rise to new antigenic determinants. Recognition requires separate, specific antibodies.[ citation needed ]

See also

Related Research Articles

<span class="mw-page-title-main">Antigen</span> Molecule triggering an immune response (antibody production) in the host

In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.

<span class="mw-page-title-main">Antibody</span> Protein(s) forming a major part of an organisms immune system

An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an antigen. Each tip of the "Y" of an antibody contains a paratope that is specific for one particular epitope on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize it directly.

<span class="mw-page-title-main">Human leukocyte antigen</span> Genes on human chromosome 6

The human leukocyte antigen (HLA) system or complex is a complex of genes on chromosome 6 in humans which encode cell-surface proteins responsible for regulation of the immune system. The HLA system is also known as the human version of the major histocompatibility complex (MHC) found in many animals.

<span class="mw-page-title-main">Antigen-presenting cell</span> Cell that displays antigen bound by MHC proteins on its surface

An antigen-presenting cell (APC) or accessory cell is a cell that displays antigen bound by major histocompatibility complex (MHC) proteins on its surface; this process is known as antigen presentation. T cells may recognize these complexes using their T cell receptors (TCRs). APCs process antigens and present them to T-cells.

<span class="mw-page-title-main">T-cell receptor</span> Protein complex on the surface of T cells that recognises antigens

The T-cell receptor (TCR) is a protein complex found on the surface of T cells, or T lymphocytes, that is responsible for recognizing fragments of antigen as peptides bound to major histocompatibility complex (MHC) molecules. The binding between TCR and antigen peptides is of relatively low affinity and is degenerate: that is, many TCRs recognize the same antigen peptide and many antigen peptides are recognized by the same TCR.

<span class="mw-page-title-main">Epitope mapping</span> Identifying the binding site of an antibody on its target antigen

In immunology, epitope mapping is the process of experimentally identifying the binding site, or epitope, of an antibody on its target antigen. Identification and characterization of antibody binding sites aid in the discovery and development of new therapeutics, vaccines, and diagnostics. Epitope characterization can also help elucidate the binding mechanism of an antibody and can strengthen intellectual property (patent) protection. Experimental epitope mapping data can be incorporated into robust algorithms to facilitate in silico prediction of B-cell epitopes based on sequence and/or structural data.

In academia, computational immunology is a field of science that encompasses high-throughput genomic and bioinformatics approaches to immunology. The field's main aim is to convert immunological data into computational problems, solve these problems using mathematical and computational approaches and then convert these results into immunologically meaningful interpretations.

<span class="mw-page-title-main">Linear epitope</span> Segment of a molecule which antibodies recognize by its linear structure

In immunology, a linear epitope is an epitope—a binding site on an antigen—that is recognized by antibodies by its linear sequence of amino acids. In contrast, most antibodies recognize a conformational epitope that has a specific three-dimensional shape.

Bacterial display is a protein engineering technique used for in vitro protein evolution. Libraries of polypeptides displayed on the surface of bacteria can be screened using flow cytometry or iterative selection procedures (biopanning). This protein engineering technique allows us to link the function of a protein with the gene that encodes it. Bacterial display can be used to find target proteins with desired properties and can be used to make affinity ligands which are cell-specific. This system can be used in many applications including the creation of novel vaccines, the identification of enzyme substrates and finding the affinity of a ligand for its target protein.

Immunogenicity is the ability of a foreign substance, such as an antigen, to provoke an immune response in the body of a human or other animal. It may be wanted or unwanted:

<span class="mw-page-title-main">Paratope</span> Part of an antibody which binds to an antigen

In immunology, a paratope, also known as an antigen-binding site, is the part of an antibody which recognizes and binds to an antigen. It is a small region at the tip of the antibody's antigen-binding fragment and contains parts of the antibody's heavy and light chains. Each paratope is made up of six complementarity-determining regions - three from each of the light and heavy chains - that extend from a fold of anti-parallel beta sheets. Each arm of the Y-shaped antibody has an identical paratope at the end.

Molecular mimicry is the theoretical possibility that sequence similarities between foreign and self-peptides are enough to result in the cross-activation of autoreactive T or B cells by pathogen-derived peptides. Despite the prevalence of several peptide sequences which can be both foreign and self in nature, just a few crucial residues can activate a single antibody or TCR. This highlights the importance of structural homology in the theory of molecular mimicry. Upon activation, these "peptide mimic" specific T or B cells can cross-react with self-epitopes, thus leading to tissue pathology (autoimmunity). Molecular mimicry is one of several ways in which autoimmunity can be evoked. A molecular mimicking event is more than an epiphenomenon despite its low probability, and these events have serious implications in the onset of many human autoimmune disorders.

<span class="mw-page-title-main">Complementarity-determining region</span> Part of the variable chains in immunoglobulins and T cell receptors

Complementarity-determining regions (CDRs) are part of the variable chains in immunoglobulins (antibodies) and T cell receptors, generated by B-cells and T-cells respectively, where these molecules bind to their specific antigen. A set of CDRs constitutes a paratope. As the most variable parts of the molecules, CDRs are crucial to the diversity of antigen specificities generated by lymphocytes.

<span class="mw-page-title-main">Polyclonal B cell response</span> Immune response by adaptive immune system

Polyclonal B cell response is a natural mode of immune response exhibited by the adaptive immune system of mammals. It ensures that a single antigen is recognized and attacked through its overlapping parts, called epitopes, by multiple clones of B cell.

Human leukocyte histocompatibility complex DO (HLA-DO) is an intracellular, dimeric non-classical Major Histocompatibility Complex (MHC) class II protein composed of α- and β-subunits which interact with HLA-DM in order to fine tune immunodominant epitope selection. As a non-classical MHC class II molecule, HLA-DO is a non-polymorphic accessory protein that aids in antigenic peptide chaperoning and loading, as opposed to its classical counterparts, which are polymorphic and involved in antigen presentation. Though more remains to be elucidated about the function of HLA-DO, its unique distribution in the mammalian body—namely, the exclusive expression of HLA-DO in B cells, thymic medullary epithelial cells, and dendritic cells—indicate that it may be of physiological importance and has inspired further research. Although HLA-DM can be found without HLA-DO, HLA-DO is only found in complex with HLA-DM and exhibits instability in the absence of HLA-DM. The evolutionary conservation of both DM and DO, further denote its biological significance and potential to confer evolutionary benefits to its host.

<span class="mw-page-title-main">Conformational epitope</span> Segment of a molecule which contacts an immune receptor when folded

In immunology, a conformational epitope is a sequence of sub-units composing an antigen that come in direct contact with a receptor of the immune system.

Peptide-based synthetic vaccines are subunit vaccines made from peptides. The peptides mimic the epitopes of the antigen that triggers direct or potent immune responses. Peptide vaccines can not only induce protection against infectious pathogens and non-infectious diseases but also be utilized as therapeutic cancer vaccines, where peptides from tumor-associated antigens are used to induce an effective anti-tumor T-cell response.

Immunomics is the study of immune system regulation and response to pathogens using genome-wide approaches. With the rise of genomic and proteomic technologies, scientists have been able to visualize biological networks and infer interrelationships between genes and/or proteins; recently, these technologies have been used to help better understand how the immune system functions and how it is regulated. Two thirds of the genome is active in one or more immune cell types and less than 1% of genes are uniquely expressed in a given type of cell. Therefore, it is critical that the expression patterns of these immune cell types be deciphered in the context of a network, and not as an individual, so that their roles be correctly characterized and related to one another. Defects of the immune system such as autoimmune diseases, immunodeficiency, and malignancies can benefit from genomic insights on pathological processes. For example, analyzing the systematic variation of gene expression can relate these patterns with specific diseases and gene networks important for immune functions.

<span class="mw-page-title-main">Peptide microarray</span>

A peptide microarray is a collection of peptides displayed on a solid surface, usually a glass or plastic chip. Peptide chips are used by scientists in biology, medicine and pharmacology to study binding properties and functionality and kinetics of protein-protein interactions in general. In basic research, peptide microarrays are often used to profile an enzyme, to map an antibody epitope or to find key residues for protein binding. Practical applications are seromarker discovery, profiling of changing humoral immune responses of individual patients during disease progression, monitoring of therapeutic interventions, patient stratification and development of diagnostic tools and vaccines.

Antigen-antibody interaction, or antigen-antibody reaction, is a specific chemical interaction between antibodies produced by B cells of the white blood cells and antigens during immune reaction. The antigens and antibodies combine by a process called agglutination. It is the fundamental reaction in the body by which the body is protected from complex foreign molecules, such as pathogens and their chemical toxins. In the blood, the antigens are specifically and with high affinity bound by antibodies to form an antigen-antibody complex. The immune complex is then transported to cellular systems where it can be destroyed or deactivated.

References

  1. ↑ Mahmoudi Gomari, Mohammad; Saraygord-Afshari, Neda; Farsimadan, Marziye; Rostami, Neda; Aghamiri, Shahin; Farajollahi, Mohammad M. (1 December 2020). "Opportunities and challenges of the tag-assisted protein purification techniques: Applications in the pharmaceutical industry". Biotechnology Advances. 45: 107653. doi:10.1016/j.biotechadv.2020.107653. PMID   33157154. S2CID   226276355.
  2. ↑ Huang J, Honda W (April 2006). "CED: a conformational epitope database". BMC Immunology. 7: 7. doi: 10.1186/1471-2172-7-7 . PMC   1513601 . PMID   16603068.
  3. ↑ Anfinsen CB (July 1973). "Principles that govern the folding of protein chains". Science. 181 (4096): 223–230. Bibcode:1973Sci...181..223A. doi:10.1126/science.181.4096.223. PMID   4124164.
  4. ↑ Bergmann CC, Tong L, Cua R, Sensintaffar J, Stohlman S (August 1994). "Differential effects of flanking residues on presentation of epitopes from chimeric peptides". Journal of Virology. 68 (8): 5306–5310. doi:10.1128/JVI.68.8.5306-5310.1994. PMC   236480 . PMID   7518534.
  5. ↑ Bergmann CC, Yao Q, Ho CK, Buckwold SL (October 1996). "Flanking residues alter antigenicity and immunogenicity of multi-unit CTL epitopes". Journal of Immunology. 157 (8): 3242–3249. doi: 10.4049/jimmunol.157.8.3242 . PMID   8871618. S2CID   24717835.
  6. ↑ Briggs S, Price MR, Tendler SJ (1993). "Fine specificity of antibody recognition of carcinoma-associated epithelial mucins: antibody binding to synthetic peptide epitopes". European Journal of Cancer. 29A (2): 230–237. doi:10.1016/0959-8049(93)90181-E. PMID   7678496.
  7. ↑ Craig L, Sanschagrin PC, Rozek A, Lackie S, Kuhn LA, Scott JK (August 1998). "The role of structure in antibody cross-reactivity between peptides and folded proteins". Journal of Molecular Biology. 281 (1): 183–201. doi:10.1006/jmbi.1998.1907. PMID   9680484.
  8. ↑ Ferdous, Saba; Kelm, Sebastian; Baker, Terry S.; Shi, Jiye; Martin, Andrew C. R. (1 October 2019). "B-cell epitopes: Discontinuity and conformational analysis". Molecular Immunology. 114: 643–650. doi:10.1016/j.molimm.2019.09.014. PMID   31546099. S2CID   202747810.
  9. ↑ Steers NJ, Currier JR, Jobe O, Tovanabutra S, Ratto-Kim S, Marovich MA, et al. (June 2014). "Designing the epitope flanking regions for optimal generation of CTL epitopes". Vaccine. 32 (28): 3509–3516. doi:10.1016/j.vaccine.2014.04.039. PMID   24795226.
  10. ↑ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). Molecular biology of the cell (4th ed.). New York: Garland Science. p. 1401. ISBN   978-0815332183.
  11. 1 2 3 4 5 6 Sanchez-Trincado, Jose L.; Gomez-Perosanz, Marta; Reche, Pedro A. (2017). "Fundamentals and Methods for T- and B-Cell Epitope Prediction". Journal of Immunology Research. 2017: 1–14. doi: 10.1155/2017/2680160 . PMC   5763123 . PMID   29445754.
  12. ↑ El-Manzalawy Y, Honavar V (November 2010). "Recent advances in B-cell epitope prediction methods". Immunome Research. 6 (Suppl 2): S2. doi: 10.1186/1745-7580-6-S2-S2 . PMC   2981878 . PMID   21067544.
  13. 1 2 3 4 5 Regenmortel, Marc H.V. (2009). "What is a B-Cell Epitope?". Epitope Mapping Protocols. Methods in Molecular Biology. Vol. 524. pp. 3–20. doi:10.1007/978-1-59745-450-6_1. ISBN   978-1934115176. PMID   19377933.
  14. ↑ Koren, E.; Groot, Anne De; Jawa, V.; Beck, K.; Boone, T.; Rivera, D.; Li, L.; Mytych, D.; Koscec, M.; Weeraratne, D.; Swanson, S.; Martin, W. (1 January 2007). "Clinical validation of the 'in silico' prediction of immunogenicity of a human recombinant therapeutic protein". Institute for Immunology and Informatics Faculty Publications. 124 (1): 26–32. doi:10.1016/j.clim.2007.03.544. PMID   17490912. S2CID   12867280.
  15. ↑ De Groot, Anne S.; Martin, William (May 2009). "Reducing risk, improving outcomes: Bioengineering less immunogenic protein therapeutics". Clinical Immunology. 131 (2): 189–201. doi:10.1016/j.clim.2009.01.009. PMID   19269256.
  16. ↑ Peters, Bjoern; Nielsen, Morten; Sette, Alessandro (26 April 2020). "T Cell Epitope Predictions". Annual Review of Immunology. 38 (1): 123–145. doi:10.1146/annurev-immunol-082119-124838. PMID   32045313. S2CID   211085860.
  17. 1 2 Ahmad, Tarek A.; Eweida, Amrou E.; El-Sayed, Laila H. (December 2016). "T-cell epitope mapping for the design of powerful vaccines". Vaccine Reports. 6: 13–22. doi:10.1016/j.vacrep.2016.07.002.
  18. 1 2 3 4 5 6 7 8 9 10 Potocnakova, Lenka; Bhide, Mangesh; Pulzova, Lucia Borszekova (2016). "An Introduction to B-Cell Epitope Mapping and In Silico Epitope Prediction". Journal of Immunology Research. 2016: 1–11. doi: 10.1155/2016/6760830 . PMC   5227168 . PMID   28127568.
  19. ↑ Davidson, Edgar; Doranz, Benjamin J. (September 2014). "A high-throughput shotgun mutagenesis approach to mapping B-cell antibody epitopes". Immunology. 143 (1): 13–20. doi:10.1111/imm.12323. PMC   4137951 . PMID   24854488.
  20. 1 2 Ahmad, Tarek A.; Eweida, Amrou E.; Sheweita, Salah A. (2016). "B-cell epitope mapping for the design of vaccines and effective diagnostics". Trials in Vaccinology. 5: 71–83. doi: 10.1016/j.trivac.2016.04.003 .
  21. ↑ Walker J, Rapley R (2008). Molecular bio-methods handbook. Humana Press. p. 467. ISBN   978-1603273749.
  22. ↑ Novus, Biologicals. "OLLAS Epitope Tag". Novus Biologicals. Retrieved 23 November 2011.
  23. ↑ Zakeri B, Fierer JO, Celik E, Chittock EC, Schwarz-Linek U, Moy VT, Howarth M (March 2012). "Peptide tag forming a rapid covalent bond to a protein, through engineering a bacterial adhesin". Proceedings of the National Academy of Sciences of the United States of America. 109 (12): E690–697. Bibcode:2012PNAS..109E.690Z. doi: 10.1073/pnas.1115485109 . PMC   3311370 . PMID   22366317.
  24. ↑ Correia BE, Bates JT, Loomis RJ, Baneyx G, Carrico C, Jardine JG, et al. (March 2014). "Proof of principle for epitope-focused vaccine design". Nature. 507 (7491): 201–206. Bibcode:2014Natur.507..201C. doi:10.1038/nature12966. PMC   4260937 . PMID   24499818.
  25. ↑ McBurney SP, Sunshine JE, Gabriel S, Huynh JP, Sutton WF, Fuller DH, et al. (June 2016). "Evaluation of protection induced by a dengue virus serotype 2 envelope domain III protein scaffold/DNA vaccine in non-human primates". Vaccine. 34 (30): 3500–3507. doi:10.1016/j.vaccine.2016.03.108. PMC   4959041 . PMID   27085173.
  26. 1 2 3 4 5 6 Parvizpour, Sepideh; Pourseif, Mohammad M.; Razmara, Jafar; Rafi, Mohammad A.; Omidi, Yadollah (June 2020). "Epitope-based vaccine design: a comprehensive overview of bioinformatics approaches". Drug Discovery Today. 25 (6): 1034–1042. doi:10.1016/j.drudis.2020.03.006. PMID   32205198. S2CID   214629963.
  27. ↑ Hans-Werner V (2005). "Neoantigen-Forming Chemicals". Encyclopedic Reference of Immunotoxicology. p. 475. doi:10.1007/3-540-27806-0_1063. ISBN   978-3540441724.
  28. ↑ Neoantigen. (n.d.) Mosby's Medical Dictionary, 8th edition. (2009). Retrieved February 9, 2015 from Medical Dictionary Online

Epitope prediction methods

Epitope databases

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.