What is Trimerization?

Trimerization is a chemical reaction that uses three identical molecules to produce a single trimer product. Trimerization has implications for both biological processes of clinical relevance and the industrial production of various chemicals.

Collagen is a product of trimerization. Image Credit: nobeastsofierce / Shutterstock.com

What is a trimer?

In chemistry, a trimer can be a molecular or an anion that is the product of three identical molecular or ionic precursors. The reaction responsible for producing trimers is known as trimerization, which is favored under extreme conditions and when strong bases are present.

Collagen, which is the most abundant protein present within the human body, is a product of trimerization, during which the triplex helix comprised of Gly-Xaa-Yaa peptide repeats is formed to provide the high tensile strength and stability that is associated with collagen fibers. In addition to its role in certain biological processes, the trimerization of certain chemicals is also critical for the production of many industrial substances.

Industrial trimerization processes

Polyoxymethylenes (POMs) like acetal, polyacetal and polyformaldehyde are engineered thermoplastics that are often used in precision parts as a result of their high stiffness, low frictional and impressive dimensional stability.

One of the most important industrial processes that is used to produce POMs is the trimerization of formaldehyde, which leads to the production of the trimer intermediate of 1,3,5-trioxane.

Aside from POMs, trimerization has also been applied to the production of premium quality diesel products, such as those that are used for aviation and diesel fuels. More specifically, liquid-phase trimerization has been applied to both 2-methyl-1-butene and 2-methyl-2-butene mixtures over solid acid catalysts, which have been used to produce olefins that can increase the production capacity of high-quality diesel products.

Trimerization in biology

Outside of natural biological processes, trimerization is also often used within the laboratory for clinical purposes. Some of the most notable applications of this highly versatile chemical reaction include the development of novel antibody-based therapeutic agents, stabilization of viruses like the human immunodeficiency virus type 1 (HIV-1) as well as adding to current knowledge on the mechanisms of infection by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Antibody-based therapeutics

Since its discovery in 1975, hybridoma technology has dramatically transformed the way in which highly specific monoclonal antibodies (mAbs) are produced for research, diagnostic and therapeutic purposes. To date, a total of forty-three therapeutic mAbs have been approved by both the United States Food and Drug Administration and the European Medicines Evaluation (EMA) Agency in the European Union.

Although hybridoma technology has produced many different therapeutic mAbs that are generally well-tolerated and effective for their clinical indications, they can be associated with certain limitations that can include insufficient pharmacokinetic activity, inadequate tissue accessibility and undesirable Fc-mediated interactions.

In an effort to overcome these limitations, many antibody-focused scientists have diverted their attention to developing the next generation of antibody-based therapeutics. For example, a novel intramolecular trimerization strategy has recently been discussed as a rapid and efficient method for the engineering of both mono- and multispecific trivalent antibodies.

This process begins with the fusion of single-chain variable fragments (scFv) with collagen-derived trimerization (TIE) domains that are made up of the N-terminal trimerization region of collagen XVIII NC1 or collagen XV NC1 flanked by flexible peptide linkers.

The fusing of these molecules subsequently produces monospecific trivalent trimerbodies, as well as monospecific or bispecific hexavalent trimerbodies that were expressed and excreted by mammalian cells. Each of the antibodies produced through this trimerization technique was found to exhibit good biophysical properties, effectively bind to target antigens and even inhibit the proliferation of human epidermoid carcinoma A431 cells.

HIV

In addition to being the only viral protein to protrude from the HIV-1 virion membrane, the envelope protein (Env) complex is also crucial for viral infectivity, thus causing this protein to be a major target for the host humoral immune response to HIV.

HIV particles in the bloodstream. Image Credit: Spectral-Design / Shutterstock.com

The virion-associated HIV-1 Env, as well as the Env of the simian immunodeficiency virus (SIV), both exhibit an almost exclusive trimeric structure. Therefore, the development of potentially neutralizing antibodies against this envelope protein has been focused on those that are also of a trimeric structure.

Both biochemical and biophysical methods have been used to support the stable trimerization of gp140, which is the precursor molecule to Env, for its potential antigenicity and immunogenicity.

COVID-19

On the surface of the SARS-CoV-2 virion exists spike (S) glycoproteins, which mediates the attachment, fusion and entry of the virus into a host cell and is also responsible for inducing the secretion of neutralizing antibodies.

Previous studies on the infecting cycle of the transmissible gastroenteritis coronavirus (TGEV), which also contains S glycoproteins that are closely similar to those of SARS-CoV-2, indicate that the assembly of protomers of the S glycoprotein into their bioactive trimeric structure that is comprised of three identical S glycoprotein protomers is a rate-limiting step.

With this information in mind, researchers at the University of Siena in Siena, Italy discovered that it is possible to interfere with the COVID-19 life cycle by interfering with the trimerization of the S glycoprotein of the SARS-CoV-2.

Sources

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Alvarez-Cienfuegos, A., Nuñez-Prado, N., Compte, M., et al. (2016). Intramolecular trimerization, a novel strategy for making multispecific antibodies with controlled orientation of antigen binding domains. Nature Scientific Reports 6(28643). doi:10.1038/srep28643.
Center, R. J., Lebowitz, J., Leapman, R. D., & Moss, B. (2004). Promoting Trimerization of Soluble Human Immunodeficiency Virus Type 1 (HIV-1) Env through the Use of HIV-1/Simian Immunodeficiency Virus Chimeras. Journal of Virology 78(5); 2265-2276. doi:10.1128/JVI.78.5.2265-2276.2004.
Bongini, P., Trezza, A., Bianchini, M., et al. (2020). A possible strategy to fight COVID-19: Interfering with spike glycoprotein trimerization. Biochemical and Biophysical Research Communications 528(1); 35-38. doi:10.1016/j.bbrc.2020.04.007.

What is a trimer?

Industrial trimerization processes

Trimerization in biology

Antibody-based therapeutics

HIV

COVID-19

Sources

Further Reading

Benedette Cuffari