Actin Polymerization Dynamics - Insights from In vitro TIRF Microscopy

Abstract

Actin elongation is a bi-molecular reaction between monomeric actin (G-actin) and filamentous actin (F-actin), in the first approximation. It can be controlled by changing the ability of either G-actin or F-actin to participate in the reaction. Either of the two mechanisms alone is not sufficient to maintain a large pool of G-actin ready to polymerize in a signal-controlled fashion [1]. Mammalian cells have hundreds of actin-binding proteins (ABP) which bind either or both the forms of actin. Profilin sequesters G-actin and makes them pre-disposed towards F-actin barbed-end addition, cofilin severs F-actin and deploymerizes it into G-actin. On the other hand, capping protein (CP) caps the barbed-end and stops further elongation of F-actin [2]. Gelsolin-family of proteins [3] sever F-actin as well as cap filaments. In vitro TIRF microscopy [4] has been used to monitor real-time actin dynamics in the presence of ABPs [5], [6]. Representative results on some ABPs which alter actin assembly will be presented.