Synapses represent key transduction machines that convert action potential-based signals into secreted chemical messages which in turn are converted back into postsynaptic electrical responses. Modulation of these processes is thought to underlie critical mechanisms of learning and memory, and dysfunction of synaptic communication is suspected to be central in a number of diseased states of brain function. It has long been known that the critical trigger for neurotransmitter release is the opening of voltage-gated calcium channels within the presynaptic terminal which in turn leads to the influx of calcium. The highly-non-linear relationship between calcium entry and exocytosis efficiency places the control of calcium channel function and abundance as a potent potential leverage point in sculpting synaptic strength. We recently demonstrated that expression of a calcium channel subunit, alpha2delta, is rate-limiting in determining how many calcium channels are present at nerve terminals in hippocampal neurons. Our work showed that it acts at 2 distinct molecular steps: it acts in a forward trafficking step to allow calcium channels to traffic to synapses and it acts locally at nerve terminals to allow channels to function at the presynaptic membrane. This second step requires the integrity of a predicted domain within alpha2delta that encodes a metal-ion-dependent adhesion site. In many other proteins this domain confers binding to an extracellular partner. We predict that proper alpha2delta function requires interaction with an as-yet-discovered binding partner on the synaptic surface. The goal of this proposal is to use biochemical approaches to identify this(ese) binding partner(s).
Synaptic transmission is an essential feature of neurological and mental health. The majority of synaptic transmission occurs through chemical synapses that rely on the conversion of an electrical signal into a chemical message, delivered in the form of packets of neurotransmitters. One of the key molecules that drive this conversion is the family of voltage-gated calcium channels that are present at every nerve terminal. Their importance in this process is paramount and their dysfunction is known to result in a number of disorders including migraine and movement disorders. Additionally one of the subunits of voltage-gated calcium channels (called alpha 2 delta) is also the target of one of the most commonly used analgesics for neuropathic pain (pregabalin or Lyrica). Interestingly this protein family is likely found at all synapses, yet the drug is used for neuropathic pain. My lab recently discovered that these proteins carry out two distinct functions: they help determine how many calcium channels are present at synapses (and therefore the strength of a synapse) and they determine, once a channel is at a synapse, whether it can do its job there. This last step we think requires the protein to interact with an unknown partner, and we showed that if you change just 3 amino acids in alpha2delta it only allows the protein get channels to synapses but they cannot function because they can't interact with the presumed partner anymore. The goal of the project we propose is to identify who alpha2delta is interacting with at synapses using modern biochemical approaches. Such identification could lead to a much better understanding of how Lyrica works and why it works only at some synapses.
