Non-enzymatic proteins are able to bind to various molecules and perform vital functions, but unlike enzymes, they do not catalyze reactions. The rest of this unit discusses a non-comprehensive list of functions of non-enzymatic protein functions.
Receptors are proteins that bind to signalling molecule (ligand) to perform a cellular function. For example, upon binding of a ligand to a receptor, a ligand-gated ion channel can open, allowing the influx of ions into a cell. The following figure depicts this example:
Additionally, there are other types of receptors such as G-Protein Coupled Receptors (GPCRs) and Receptor Tyrosine Kinases (RTKs).
These proteins bind to molecules with high affinity in areas of high concentration and low affinity in areas of low concentration to transport them to other locations. This allows the protein to bind to molecules where there is a high concentration and transport then release them in areas where there is low concentration. A great example of a transport protein is hemoglobin which mainly transports oxygen throughout the body. More about hemoglobin will be discussed in the respiratory physiology sections.
These proteins are required for motility within cells. Examples include myosin (muscle contraction), kinesin (intracellular transport), and dynein (intracellular transport and cilia motility).
Antibodies are essential components of the immune system. They are required to bind to their ligand, antigens, with extremely high affinity. The antigens are found on molecules which the immune system considers harmful.