The lock-and-key principle describes a system of complementary structures that interlock like a key in a lock and trigger certain body processes with this complex formation. The principle is also known as the hand-in-glove principle or induced-fit concept and plays a role for all receptor-substrate complexes. The principle is also crucial for pathological processes such as infections with viruses.
What is the lock-and-key principle?
The lock-and-key principle describes a system of complementary structures that interlock like a key in a lock and trigger certain body processes with this complex formation. The principle is also decisive, for example, for pathological processes such as infections with viruses. A key fits with its structures with extreme accuracy into the corresponding lock. As soon as one prong is broken off, the door no longer opens. In this context, we also talk about accuracy of fit. Just as the key fits into the lock, many biological messenger substances fit exactly into the structures of the receptors provided for them. In the larger context, the so-called lock-and-key principle of biology refers to two or more complementary structures with a spatial fit to each other. This fit is associated with biochemical reactions. The lock-and-key principle was first described in 1894 by Emil Fischer, who at that time described a hypothetical binding of enzymes and substrates. In biology and biochemistry, the interactive binding between guest ligand and receptor host results in a complex with a certain binding strength, also known as affinity. Instead of the lock-and-key principle, these relationships are now also referred to as the induced-fit concept or hand-in-glove principle. In most cases, guest ligands are effective in complex formation only through certain parts of their overall structure. In this case, their remaining structures are functionally irrelevant for complex formation and the effects provoked by it.
Function and task
The lock-and-key principle plays a role in biochemistry and biology in entirely different contexts. In biochemistry, transmitters and modulators, by binding to a receptor, trigger biochemical processes that can be simulated or blocked by drugs or pharmaceuticals. For such bindings, the lock-and-key principle plays an essential role. In endocrinology, on the other hand, there is an interaction between hormone receptors and individual hormones that triggers signal chains and has a feedback effect on cell function. The lock-and-key principle is also relevant in this context. The same applies to the field of enzymology, within which enzymes facilitate biochemical reactions. This process takes place by bringing together biogenic reactants. Enzymes thus allow two active substances to form a complex according to the lock-and-key principle. The enzyme undergoes structural changes due to substrate binding, which further enhance or enable its effectiveness as a catalyst on certain substrates. In immunology, the lock-and-key principle is equally relevant. Within this domain, complement structures interact at the boundary of antigen-recognizing and antigen-presenting cells. This complex interaction according to the lock-and-key principle is a prerequisite of specific antigen recognition. Furthermore, the lock-and-key principle plays an essential role for cells in cell assemblies such as tissues or organs. These cells are equipped with structures and their complementary counterstructures on the cell surface. This lock-and-key complementary system enables communication between cells in a tissue and contributes to structural functional cohesion. Immune cells also communicate with the help of the described complementary system. In addition, circulating immune cells depend on special surface structures to enable them to move from place to place and find their way back to their starting point. Sperm cells use a similar principle to move to the egg cell. The lock-and-key principle lets them find glycoproteins on the oocyte surface that let them enter the cell. Thus, on a larger scale, the principle plays a crucial role in human reproduction and is relevant in evolutionary biology.
Diseases and ailments
Not only for natural body processes, but also for pathological processes in the human or animal body, the lock-and-key principle is crucial. For one thing, certain substances in drugs and other substances block individual receptors according to the lock-and-key principle. Morphine, for example, switches off the coughing stimulus by having its active ingredients bind precisely to the cells in the nervous system responsible for the coughing stimulus. In addition, the substance has an analgesic effect in the same way and binds to pain receptors, particularly in the cerebral cortex, according to the lock-and-key principle. As a result of the binding, pain stimuli are no longer transmitted. So although painful stimuli are theoretically still received, they are no longer processed and no longer reach consciousness. Medicine makes use of this principle to treat patients with acute and chronic pain, such as cancer patients. On the other hand, blocking nerve cells according to the lock-and-key principle can also disrupt or switch off relevant bodily processes and thus show negative effects on a patient’s health. The lock-and-key principle is equally pathological in the context of viruses. These organisms possess certain complementary structures, also known as docking sites. It is the docking site of a virus that enables it to infect its host. The hand-in-glove principle is also of medical relevance in medical diagnostics. Diagnostic procedures such as the typing of individual tissues as part of a biopsy, the diagnosis of infections and DNA detection or blood group diagnostics are essentially based on detection using the principle. In addition, many metabolic diseases are based on a disturbance of the hand-in-glove principle. This applies, for example, to the form of diabetes mellitus in which there is complete insulin resistance. In insulin resistance, the “hand” insulin no longer fits into the “glove” insulin receptor. The cell receptors no longer respond adequately to insulin and the uptake of sugar into the individual cells occurs only to an insufficient extent. Beyond these connections, the induced-fit concept plays a significant role in everyday medical practice, for example, for vaccinations, but also for allergies.
