Researchers at the Massachusetts Institute of Technology's Picower Institute for Learning and Memory said the protein helps synapses develop, underlying our ability to learn and remember.

Now neuroscience Professor Li-Huei Tsai and colleagues have identified an enzyme that's key to that protein's activity.

Tsai studies a kinase called Cdk5. While Cdk5's best-known role is to help new neurons form and migrate to their correct positions during brain development, new evidence shows Cdk5 interacts with synapse-inducing proteins -- in particular, a protein called CASK. Mutations in the genes responsible for Cdk5 and CASK have been linked with mental retardation.

"We found Cdk5 is critical for recruiting CASK to do its job for developing synapses," Tsai said. "Without Cdk5, CASK was not in the right place at the right time, and failed to interact with essential presynaptic components. This, in turn, led to problems with calcium influx."

The study, reported in the journal Neuron, also provides the first molecular explanation of how Cdk5, which also may go awry in neurodegenerative diseases such as Alzheimer's, promotes synapse development.