  We model the dynamical states of the C-termini of tubulin dimers that
comprise neuronal microtubules. We use molecular dynamics and other
computational tools to explore the time-dependent behavior of conformational
states of a C-terminus of tubulin within a microtubule and assume that each
C-terminus interacts via screened Coulomb forces with the surface of a tubulin
dimer, with neighboring C-termini and also with any adjacent
microtubule-associated protein 2 (MAP2). Each C-terminus can either bind to the
tubulin surface via one of several positively charged regions or can be allowed
to explore the space available in the solution surrounding the dimer. We find
that the preferential orientation of each C-terminus is away from the tubulin
surface but binding to the surface may also take place, albeit at a lower
probability. The results of our model suggest that perturbations generated by
the C-termini interactions with counter-ions surrounding a MAP2 may propagate
over distances greater than those between adjacent microtubules. Thus, the MAP2
structure is able to act as a kind of biological wire (or a cable) transmitting
local electrostatic perturbations resulting in ionic concentration gradients
from one microtubule to another. We briefly discuss implications the current
dynamic modeling may have on synaptic activation and potentiation.
