It’s a term that comes up often in pharmacology, medicinal chemistry and drug development. A peptide analogue is not just another name for a natural peptide. In general, it is a modified version that is created to produce a particular effect or to improve a property of the original molecule.
What’s different about a peptide analogue?
Peptides are short chains of amino acids. The sequence and composition of these amino acids determine a peptide’s shape and biological activity. Even tiny changes in structure can affect how the molecule interacts with receptors, enzymes or other biological targets.
A peptide analogue is a peptide that has been deliberately modified but retains sufficient structure to have a useful biological relationship with the natural peptide.
For example, scientists might replace one amino acid for another, change part of the peptide backbone, or make a chemical change that would affect the stability of the molecule. Such changes may make the analogue behave differently from the naturally occurring peptide.
It’s not always a matter of making the molecule more potent. Sometimes the goal is to make it last longer, reduce unwanted activity, improve its stability or change how it interacts with a target.
Why do we make peptide analogues?
A major problem with natural peptides is that many are relatively quickly broken down in the body. Enzymes can identify peptide structures and degrade them into smaller components. This can limit the lifetime of a natural peptide.
A peptide analogue can be designed to resist this degradation.
Absorption, distribution and elimination can also be affected by structural changes. In drug development, therefore, researchers may use peptide analogues to investigate whether a modified molecule has more suitable properties than the parent peptide.
Another reason is selectiveness. A natural peptide can work at several related receptors or biological pathways. Sometimes changes in structure can alter these interactions and make an analogue more selective for a particular target.
This does not mean every change works. A change in a peptide can improve one property and affect another. For example, a more stable compound may not interact with the target in the same way as the original peptide.
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How Do Peptide Analogues Work?
The mechanism is dependent upon the specific peptide analogue and its intended target.
Some peptide analogues behave like the natural peptide. They may bind to the same receptor and elicit a similar biological response. When these activate the receptor, they are often called peptide receptor agonists.
Other analogues may antagonise or attenuate receptor activity. Depending on their particular structure and mechanism, these can act as antagonists.
There are also analogues with more complex effects. The affinity of the molecule for its receptor, the signalling after receptor binding, or the interactions with different types of receptors can be altered by modifying the structure.
Hence the word analogue refers to a structural relationship, not to one single kind of biological action.
Natural peptide vs peptide analogue
The simplest way to understand the difference is to think of the natural peptide as the starting point.
A natural peptide is a peptide that is found in a biological system and has a specific structure and function. The analogue of a peptide is deliberately changed to be similar to that peptide but with a structural difference.
It could change to:
- Replacement of one or more amino acids
- Changing the peptide backbone
- Switching the chemical groups attached to the molecule
- Altering to enhance resistance to enzymatic degradation
- Changing the molecule to affect binding to the receptor
The compound made can have some of the properties of the original peptide but different pharmacological properties.
Examples in medicine and research
Peptide analogues are being studied and developed for use in several areas of medicine.
One well-known example is desmopressin*, a synthetic version of the naturally occurring hormone vasopressin. Structural changes produce a different pattern of activity and help to make it useful in some medical settings.
Another group are analogues of the hormone somatostatin, which is involved in regulating a number of physiological processes. The natural hormone has a relatively short duration of action, and synthetic somatostatin analogues have been developed.
Also, there are peptide-based drugs related to hormones that control glucose regulation, appetite and other physiological functions. In those cases the structural changes may alter the activity of the receptor and the duration of the activity of the medicine.
The precise effect depends on the molecule. It is therefore important not to assume that all peptide analogues work in the same way.
What are the advantages and disadvantages?
One of the main benefits of peptide analogue design is the modulation of the properties of a biologically active molecule. Structural changes can be used by researchers to study stability, receptor selectivity, duration of action and other characteristics.
This is especially useful when there is good biological activity in a natural peptide, but it is not an ideal drug in the natural form.
There are also shortcomings. However, peptides can pose challenges in terms of stability, absorption and delivery. Many are not readily absorbable by mouth, as they can be degraded in the digestive system. Some, therefore, need other means of administration.
Structural change can also bring about unanticipated changes. An analogue may bind less well to its intended target, or it may interact with other biological targets. Thus each compound has to be studied on its merits rather than being judged purely on the basis of its similarity to the natural peptide.
Peptide analogues in drug development
It takes more than just tweaking a molecule to see if it works to make a peptide analogue.It is vital that researchers understand how the structural modification affects the physicochemical and physiological properties of the substance.
In vitro tests include receptor binding tests and biological activity tests, and in vivo tests include pharmacokinetics tests, which consist of absorption, distribution, metabolism, and excretion. Further studies are necessary to prove the safety and clinical usefulness of such a peptide analogue.
In simple words, a peptide analog is an altered peptide whose purpose is to retain or modify certain biological characteristics of a native peptide. The alterations can be minimal, yet the impact can be considerable. Thus, the peptide analogs are important in biological research and drug discovery.
Research Use Only. This glossary explains terminology used in published research. It is not medical advice and does not describe any product for human or animal use.