Molecular Signaling


The rationale behind phosphorylation is that kinases have the ability to phosphorylate thousands of molecules that can thus turn on many different cellular functions.  Kinases may dramatically amplify cellular activity. In the immune system, two chains of the T-cell receptor are brought together by the activation of a kinase domain.  Calmodulin may modify kinases by causing the release of calcium ions from a cell.  Phosphorylation, in and of itself, has the capability to modify the three-dimensional structure of various structures.  Src-family kinases are regulated tyrosine kinases, which also function as adapter proteins.

Another sequence, SH3 (Src Homology 3)  forms as an adapter protein itself that allows it to bind to other proteins; mainly proteins possessing a lot of prolines.  SH2 (Src Homology 2) will only bind tyrosine if it’s phosphorylated.  The SH2 domain is commonly used in immune system transduction.  SH1 (Src Homology 1) kinase has the ability to be both positively and negatively regulated.  It has within it a tyrosine.  When the tyrosine is phosphorylated, it allows this kinase to be activated.  Another tyrosine outside SH1 when phosphorylated, turns off the kinase.  If proteins have a phosphorylated tyrosine, or a proline – rich structure; these kinases can bind to a global amount of these proteins.  Proteins  that are joined together may deaggregate after the proteins are dephosphorylated.

Calmodulin is a phosphatase that normally, when phosphorylated is trapped in the cytoplasm.  However, when  it gets dephosphorylated, calmodulin can migrate into the nucleus, look for a nuclear binding region, and turn on those genes.  In the immune system, T-cell activation may be suppressed with drugs such as cyclosporin and tacrolimus.  These two drugs block the signaling of calcineurin.