Half-Site Inhibition of Kinesin-1 by a Single Tail Domain, Sometimes One is Enough

Abstract

Isolated kinesin-1 is autoinhibited through binding of a region in the C-terminal tail domain to the N-terminal head (motor) domains. Although the heavy chain dimer has two head and two tail domains, the stoichiometry of binding when expressed separately in trans is one tail peptide per two heads. Both monomeric and dimeric tail domain constructs have similar affinity for a dimer of heads, indicating that the second peptide in a tail dimer does not contribute significant additional free energy to the interaction. The recent solution of the X-ray structure (Kaan et al., Science 333, 883 (2011)) of a complex of one tail domain and a dimer of heads suggested a ‘double lockdown’ mechanism in which ADP release is likely inhibited because the coupled undocking of the neck linker cannot occur while maintaining both the cross link between heads at the coiled coil neck and the new cross link provided by the tail domain that bridges two heads. This result stimulates a number of new questions that will be addressed. If only one tail is interacting strongly with the heads, what is the other tail peptide doing? Can it bind to cargo or regulators while the other peptide remains bound to the heads? One approach is to produce heterodimer tails with mutations that allow only one peptide to bind to heads, while introducing probes into the other tail to test for its binding interactions.