About Cyclin / CCN:
Cyclin is a family of proteins that is responsible for controlling the progression of cells throughout the cell cycle. It does this by releasing cyclin dependent kinase enzymes, which is a group of enzymes necessary for cell progression.
Cyclins are very different from each other when it comes to their amino acid sequence and their primary structure. However, the cyclin box has the same or very similar 100 amino acids that make up the box which is shared throughout all of the cyclins. There are two domains of all a-fold which are located at the N-terminus and the C-terminus. Every cyclin is thought to have a similar structure of two domains of 5 a helix. Cyclins outside of the box are known to be divergent, but some are conserved inside the box.
Cyclins are responsible regulating the cell cycle. Like mentioned above, there are many different types of cyclins, some of which completely different functions from others in their family. Although, they are all important when it comes to the cell cycle and they end up producing CDKs to complete this task. Cyclins themselves do not have any enzymatic properties or activity, but they do have binding sites for some substrates and can also target CDKs to certain subcellular locations. For example, G1 cyclins are not going to have the same job as the S cyclins. Where the S cyclin will bond with the CDK and induce DNA replication, the G1 coordinates the cell growth. G1 cyclins behave differently from the others in the family, as the concentration gets higher gradually depending on the rate of cell growth, which is not how the others behave.
When cyclins interact and are bound with dependent kinases such as various proteins, they form the maturation promoting factor. These then activate other proteins through phosphorylation. These proteins then become responsible for specific events during the cell cycle, showing that each one has its own individual job.
As there are many different types of cyclin, each class will have its own function or timing in the cell cycle. It has even been thought that some of these such as Cyclin D1 can be therapeutic in targeting certain types of cancer drugs. Cyclin regulates various mechanisms throughout the cell cycle, and it depends on the cell type, as well as the cyclin type as to what these are.