Modelling Ca2+ -dependent proteins in the spine - challenges and solutions

Background / Purpose: Modelling post-synaptic proteins poses three technical problems: small absolute molecule numbers, large numbers of possible states, and the complex geometry of the spine, which is not a well-mixed compartment. Computational approaches are needed that solve all three of these problems. Main conclusion: Stochastic simulation methods can be used for systems with small molecule numbers, agent-based methods to represent multi-state molecules, and spatial methods to simulate events in complex geometries. We used the agent-based spatial stochastic simulator MCell to model the Ca2+-dependent activation of calmodulin and Ca2+/calmodulin-dependent kinase II (CaMKII) in the spine. Next steps: Next steps will include the extension of our model to include more interaction partners, and to represent some of the regulation events in more detail.