J. Biol. Chem., Vol. 261, Issue 23, 10701-10706, Aug, 1986
Acanthamoeba profilin affects the mechanical properties of nonfilamentous actin
M Sato, WH Schwarz and TD Pollard
We investigated the mechanical properties of two abundant, cytoplasmic
proteins from Acanthamoeba, profilin and actin, and found that while both
profilin and nonfilamentous actin alone behaved as solids, mixtures of the
two proteins were viscoelastic liquids. When allowed to equilibrate,
profilin formed a viscoelastic solid with mechanical properties similar to
filamentous and nonfilamentous actin. Consequently, profilin itself may
contribute significantly to the elasticity and viscosity of cytoplasm. The
addition of profilin to nonfilamentous actin caused a phase transition from
gel (viscoelastic solid) to sol (viscoelastic liquid) when the
concentration of free actin became too low to form a gel. In contrast,
profilin had little effect on the rigidity and viscosity of actin
filaments. We speculate that nonfilamentous actin and profilin, both of
which form shear- sensitive structures, can be modeled as flocculant
materials. We conclude that profilin may regulate the rigidity (elasticity)
of the cytoplasm not only by inhibiting polymerization of actin, but also
by modulating the mechanical properties of nonfilamentous actin.
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