Cyclin-dependent kinase 5 is a protein, and more specifically an enzyme, that is encoded by the Cdk5 gene. It was discovered 15 years ago, and it is saliently expressed in post-mitotic central nervous system neurons (CNS).
The molecule belongs to the cyclin-dependent kinase family. Kinases are enzymes that catalyze reactions of phosphorylation. This process allows the substrate to gain a phosphate group donated by an organic compound known as ATP. Phosphorylations are of vital importance during glycolysis, therefore, making kinases an essential part of the cell due to their role in the metabolism, cell signaling, and many other processes.
Cdk5 is a proline-directed serine/threonine kinase, which was first identified as a CDK family member due to its similar structure to CDC2/CDK1 in humans, a protein that plays a crucial role in the regulation of the cell cycle.
The gene Cdk5 contains 12 exons in a region that contains around 5000 nucleotides (5kb), as it was determined by Ohshima after cloning the Cdk5 gene that belonged to a mouse.
Cdk5 has 292 amino acids and presents both α-helix and β strand structures.
Even though Cdk5 has a similar structure to other cyclin-dependent kinases, its activators are highly specific (CDK5R1 and CDK5R2).
Some investigations have reported that the active states of protein kinases structurally differ from each other in order to preserve the geometry of its machinery so that catalytic output works properly. The Cdk5 kinase has an original design as well.
Cdk5 belongs to the eukaryotic protein kinases (ePKs). A crystal structure of the catalytic domain of cAMP-dependent protein kinase showed that it holds 2 lobes; on the one hand, it has a small lobe, an N-terminal arranged as an antiparallel β-sheet structure. Furthermore, it contains nucleotide motifs as a way to orient the nucleotide for phospho-transfer. On the other hand, the large lobe, a C-terminal, is helical shaped, which helps to identify the substrate and includes crucial residues for the phospho-transfer.