Cyclin-dependent kinase, or CDK, is a type of enzymatic protein that resides in eukaryotic cells and plays a key role in cellular metabolism and renewal, a series of biological processes collectively referred to as the cell cycle. Several protein kinases are also classified as genes, making up about 2 percent of all human genes. The mechanism of CDK activity is based on phosphorylation, or the process of contributing phosphate groups to substrate proteins. However, in order for a protein to be modified by phosphorylation, it must form a complex with another kind of protein known as cyclin. This is why this particular specialized protein is termed cyclin-dependent kinase.
Aside from regulating cellular function, the other significant activity associated with cyclin-dependent kinase is providing the pathway for signal transduction. In other words, cells are able to communicate with each other by enlisting CDK enzymes to serve as chemical messengers. While this process may be fascinating to biology enthusiasts, it is of primary interest to the medical community due to its implication in the development of disease. In fact, impaired signal transduction is considered largely responsible for the onset of many diseases, including heart disease, diabetes, cancer, and many auto-immune disorders.
One of the most promising applications regarding the treatment of such diseases is the possibility of intercepting cyclin-dependent kinase activity in cells. In fact, a few medications designed to target and inhibit CDK have been shown to promote apoptosis, or cellular death. This result is particularly significant in terms of combating tumor growth and the spread of cancer. In addition, these drugs appear to affect neutrophil granulocytes, which contribute to the development of chronic inflammatory conditions such as arthritis. However, since these drugs may also impact the cyclin-dependent kinase mediated pathway and lead to unwanted side effects, more research is needed to ensure only receptor cells are targeted.
There are also different kinds of CDK proteins that may be targeted to help prevent a variety of reactions. For example, inhibiting cyclin-dependent kinase 2 may help to deter hair loss that often occurs while being treated with chemotherapy, while manipulating cyclin-dependent kinase 4 may impact the regulation of Rb, a protein linked to tumor suppression.
Protein kinases also work differently toward cellular regulation. While each type initiates phosphorylation by borrowing a phosphate group from adenosine-5-triphosphate (ATP), it must also be able to attach the phosphates to an available hydroxyl group belonging to one of three amino acids. The majority of kinases accomplish this by selecting the amino acids serine and threonine, while others seek out tyrosine. However, there are a few that are compatible with all three.