Data from: Regulation of the formin INF2 by actin monomers and calcium-calmodulin

In response to increased intracellular calcium, the formin INF2
polymerizes 20-30% of the total cellular actin pool within 30 sec,
suggesting robust regulation. INF2 regulation requires an
auto-inhibitory interaction between the N-terminal Diaphanous Inhibitory
Domain (DID) and the C-terminal Diaphanous Auto-regulatory Domain
(DAD). DID mutations are dominantly linked to two human diseases
and constitutively activate INF2. However, DAD binding to actin
monomers competes with DID binding, disrupting regulation. Here,
we use a novel cell-free assay for detailed investigation of INF2
regulation. Contrary to our previous findings, INF2 inhibition
does not require CAP proteins but does require actin ‘buffering’ by
monomer-binding proteins such as profilin or thymosin. INF2 is activated
by calcium-bound calmodulin (CALM) through CALM binding to the N-terminus.
In addition, the N-terminus plays an important role in INF2 regulation
beyond CALM binding. These findings support a role for actin
monomer binding proteins in not only regulating overall actin dynamics but
also in specific regulation of an actin polymerization factor.