Magazine article Science News

Molecular Switch Makes Memory Stick

Magazine article Science News

Molecular Switch Makes Memory Stick

Article excerpt

How unstable molecules can store information stably has long baffled scientists. Human long-term memory may depend on such a mechanism. Recently, a biologist at Brandeis University in Waltham, Mass., proposed a theoretical model for a molecular "switch," made up of two enzymes with opposite actions. The system could store information indefinitely despite continual turnover of the individual molecules that make up the switch.

John E. Lisman describes in the May (Number 9) PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES a hypothetical chemical switch made of a kinase (an enzyme that catalyzes phosphate group transfer to form triphosphates like ATP) and a phosphatase (an enzyme that cleaves a phosphate group from a molecule). The switch is bistable, Lisman says, because it can be either "on" or "off" but is never in between. It is local, he says, because it could be located in specific compartments of neurons -- such as dendrites, the spiny processes that conduct impulses to other neurons -- rather than centralized in DNA of the cell nucleus.

In his paper, Lisman discusses how this molecular switch could be turned on permanently by an external stimulus. In the "off" state, the kinase, which Lisman calls kinase-1, is unphosphorylated and inactive. A stimulus such as a protein binding to a receptor on a cell membrane, Lisman says, could activate a second kinase, kinase-2, which phosphorylates kinase-1. Kinase-1 is activated briefly until the phosphatase removes a phosphate group and returns kinase-1 to its inactive state.

When kinase-2 stimulation reaches a critical level, kinase-1 becomes activated permanently. Phosphorylation of kinase-1 happens faster than phosphatase can reverse it, and kinase-1 starts to phosphorylate and activate other kinase-1 molecules. Thus, even if the stimulus is removed and kinase-2 activity is eliminated, kinase-1 activity continues. …

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