Think about the last time you were at the doctor’s office or in the hospital. Were you tested for coronavirus or another illness? Did you or your child get a vaccination? Perhaps you had a deep cut that needed stitches to stop the bleeding. Do you have diabetes and use insulin to manage your blood sugar? Maybe you or someone you know uses special treatments to battle cancer.
Purified proteins are used in all of these remarkable medical applications, and in many more! In this article we will consider the ways that purified proteins are currently used in medical care and discuss the transformative applications that are coming in the future.
Six common medical applications of purified proteins are:
- diabetes drugs
- weight-loss drugs
- antibody-based drugs
- waterproof adhesives
Article Table of Contents
Diabetics administer the protein insulin to help regulate their sugar or glucose levels. Insulin was originally purified from dog pancreas in the 1920s. Insulin from this and other animal sources was used for decades to treat diabetics. However, many patients had allergic reactions to animal forms of insulin. Also, the reliability, consistency, and purity of animal-derived insulin often varied substantially.
To overcome these limitations, scientists genetically engineered bacteria to express the human form of insulin in the 1970s. This form is less allergenic, more pure, more consistently available, and removes ethical concerns for using animals to produce insulin. Check out this article for a more in depth look at the interesting discovery of insulin.
Today, recombinant insulin is taken by over 150 million diabetics worldwide (Buse et al., 2021). Recent advances include a longer-lasting insulin analog and easier administration via inhaler.
Figure 1. Insulin was traditionally purified from animal pancreas, but recombinant human protein is now expressed and purified from bacteria (PDB:1BEN; Smith et al., 1996).
Semaglutide is a peptide drug that is used to treat type 2 diabetes. A peptide is a small protein, typically less than 50 amino acids in length. Recently, semaglutide and related drugs have also been prescribed for weight loss.
Semaglutide consists of 26 amino acids that mimic the natural hormone glucagon-like peptide-1 (GLP-1). GLP-1 is released in response to food intake and stimulates insulin production. Semaglutide binds to the same hormone receptor as GLP-1, thereby increasing insulin levels even in the absence of food.
GLP-1 also reduces appetite, and in that way acts as a feedback loop to our brain – signaling that we have had enough to eat and can stop. So, semaglutide functionally uncouples the feeling of satiety (or fullness) from having eaten, allowing people to eat less and lose weight.
Figure 2. Semaglutide is a modified peptide that mimics the natural hormone GLP-1. “Aib” is alpha-aminobutyric acid, and lysine is covalently modified with stearic diacid.
In late 2019 and early 2020 we experienced a global pandemic due to the SARS CoV2 virus that shut down work, travel, and many other common gathering areas. The beginning of the pandemic was rather uncertain and frankly, scary. We did not know who was sick with the virus, or how we could protect ourselves and others when we ventured out for essential activities such as grocery shopping, or to see family and friends.
A breakthrough came when diagnostics were developed that allowed us to determine if we were infected with SARS CoV2. These devices helped us make responsible decisions about when to stay home from work, or when we could see high-risk loved ones, for example. And they helped us determine if we were sick with SARS CoV2, or something else like the common cold.
The use of these crucial medical diagnostics played a key role in dampening the spread of the global pandemic.
So how do these important devices work? They use purified antibody proteins to recognize viral proteins specific to SARS CoV2.
Figure 3. Antibodies (blue) recognizing specific sites on a coronavirus spike protein.
Proteins recognize other proteins, nucleic acids, and metabolites with incredibly high sensitivity and specificity. That’s how they perform their cellular functions, and we can leverage this feature to make powerful diagnostic devices.
However, protein-based diagnostics were in use well before the SARS CoV2 pandemic to detect the presence of specific biomolecules in developmental stages, diseases, and illnesses.
Examples of proteins used in common diagnostics include human chorionic gonadotropin for pregnancy, troponin T for myocardial infarction (heart attack), pathogen detection in infections (such as SARS CoV2), and numerous antigens in many different types of cancers.
These protein-based diagnostics play a key role in medical care. They enable us and our healthcare providers to know our current situation and help guide impactful healthcare choices.
Traditionally, vaccines used live or inactivated pathogens to train our immune systems to recognize potential invaders and rapidly tamp down future infections. However, the use of pathogens in vaccines can result in side effects, including death, when too much live pathogen is used or if a pathogen was not properly inactivated, for example.
Vaccination with purified pathogen proteins have been used since the 1980s. These proteins cannot infect patients, unlike live or improperly inactivated pathogens. This means that protein-based vaccinations have less severe side effects compared to their pathogen containing predecessors.
Examples of protein-based vaccinations include the hepatitis B vaccine, human papillomavirus, shingles (herpes zoster), and respiratory syncytial virus.
SARS CoV2 vaccines produced by Novavax and Sanofi/GSK use purified coronavirus proteins. However, Pfizer/BioNTech and Moderna vaccines use messenger RNA (mRNA).
Instead of delivering purified proteins, these vaccines deliver the mRNA message molecule that encodes for coronavirus proteins. Our cells temporarily translate this message and produce coronavirus protein for our immune system to detect.
Figure 4. mRNA from a vaccine enters the cell where ribosomes translate mRNA into proteins that lead to an immune response. The antibodies produced will also target the same proteins found on the virus the vaccine protects against.
mRNA vaccines have the advantage of faster development compared to protein vaccines.
Despite these advances, protein vaccinations will likely remain a key part of the vaccination portfolio because they are:
- established technologies in many diseases, including those described above.
- more stable and therefore easily and cheaply distributed throughout the entire world.
- more suitable for certain pathogens.
Our body produces antibodies as part of the immune response to vaccines and pathogens. Antibodies recognize and bind tightly to pathogens and their molecules to alert our immune system that clean-up is needed.
Scientists have leveraged the antibody scaffold to develop antibody-based drugs that treat cancers, autoimmune disorders, and other diseases.
Trastuzumab, which treats HER2-positive breast cancer is a well-known antibody drug. It binds to the protein receptor HER2 thereby blocking the downstream oncogenic signaling of HER2 and triggers an immune response that kills cancer cells.
Other examples of antibody drugs include adalimumab for autoimmune conditions such as rheumatoid arthritis, rituximab for non-Hodgkin’s lymphoma, and dupilumab for dermatitis and asthma.
The above examples use a basic antibody scaffold and highlight the potency of these versatile molecules! However, additional advances on the classic antibody motif have also been made and represent the next generation of antibody-based drugs, such as:
- antibody-drug conjugates used to target small-molecule drug delivery to particular organs in the body thereby limiting side effects.
- bispecific antibodies that recognize two targets at the same time, such as two different SARS-CoV2 proteins, making it harder for the target to evolve resistant mutations.
- antibody fragments and nanobodies, which due to their reduced size will have a greater ability to access targets inside of cells (traditional antibody drugs are limited to extracellular targets).
Figure 5. Trastuzumab (light orange), a breast cancer antibody drug, bound to its target protein HER2 (gray) (PDB: 1N8Z; Cho et al., 2003).
Medical adhesives are useful wound-healing devices but have limited utility in wet environments. That means their effectiveness on skin is depleted when wet, and that they are essentially useless inside the body where blood and other bodily fluids are plentiful.
However, scientists are designing the next generation of waterproof medical adhesives with inspiration from an unlikely source – sea mussels!
Mussels attach to rocks and other underwater objects using sticky, filamentous appendages called plaques (Figure 6). At the very tip of mussel plaques, proteins form the interface between mussels and the underwater objects they adhere to.
Tyrosine amino acids are particularly important for plaque proteins binding to substrates. Hydroxylation of the tyrosine side chain creates a set of atomic pinchers that clamp onto minerals, such as iron or silicone, in underwater rocks and other surfaces (Figure 6).
Scientists are designing synthetic peptides, based on mussel protein sequences, to serve as the action end of waterproof adhesives. It’s thought that these novel adhesives will have key roles including:
- surgical tissue glues to repair bleeding, tissue perforations, and fistulas.
- promoting heart regeneration after myocardial infarction.
- aiding tissue grafts for treating hernias, ulcers, and burns.
Figure 6. Mussels bind to underwater surfaces through plaque proteins. Tyrosine (Y) residues in the plaque proteins bind to mineralized surfaces.
Collectively, these medical applications illustrate the versatility of purified proteins and the wide-ranging impacts these crucial reagents have in medical care and treatment. The medical problems solved by proteins will continue to grow as we learn more about fundamental human biology, and as our ability to create novel proteins designed for specific applications increases.
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