An actin-binding protein from Acanthamoeba regulates actin filament polymerization and interactions

Abstract

A protein has been purified from Acanthamoeba which, like cytochalasin B, caps the end of actin filaments normally favoured for monomer addition and inhibits the interactions of actin filaments. In addition, this 'capping' protein nucleates the polymerization of actin monomers and blocks the annealing of actin filament fragments.

‘Cap 90’, a 90‐kDa Ca2+‐dependent F‐actin‐capping protein from vertebrate brain

“…The nevertheless rapid decrease of the low shear viscosity of F-actin at even much lower concentrations of 'cap 90' may reflect slight changes in filament lengths, too small to be detected by electron microscopy, as well as the loss of end-to-side interactions between filaments [5,17] which apparently influence the viscosity of actin networks considerably.…”

“…The low shear viscometry of actin solutions (0.5 mg/ml) was measured using the falling ball viscometer (100 ~1 capillary) of [14] as in [5].…”

“…Capping proteins bind to only one end of the actin filament [5]. If this happens to be the 'barbed', fast growing end of the actin filament, they block actin monomer addition at this end and induce a rapid depolymerization at the 'pointed', slow-growing end, due to the different critical concentrations for both ends [6].…”

Actions of cytochalasins on the organization of actin filaments and microtubules in a neuronal growth cone.

“…Cytochalasins are wellcharacterized fungal metabolites that inhibit actin polymerization by capping the barbed end of actin filaments (7,10,13,15,18,30,31,33), and that may also have other disruptive effects on actin filament networks (19,35,46). These agents are of physiological interest because they may act in a manner analogous to endogenous actin-capping proteins which have been the object of recent intense study (6,11,22,25,40).…”

Relationships between Actin Regulatory Mechanisms and Measurable State Variables

“…Barbed end specific 'capping protein' blocks assembly and disassembly at barbed ends. 24 Tropomyosin and Arp2/ 3 complex can have similar effects at pointed ends but Arp2/3 complex is most notable for its ability to nucleate new actin filaments. 38 It has recently become understood that formins represent another family of potent actin nucleators.…”