Abstract
Nickel alters the organisation of highly dynamic cytoskeletal elements. In cultured cells Ni 2+ causes microtubule aggregation and bundling as well as microfilament aggregation and redistribution. Here, we have analysed the effect(s) of Ni 2+ on in vitro actin polymerisation. Using limited proteolysis by trypsin we have suggested that the regions around Arg-62 and Lys-68 change their conformation following Ni 2+ binding to the single high-affinity site for divalent cations in the G-actin molecule. We have found that Ni 2+ shortens the lag phase of actin polymerisation and increases the rate of assembly mainly because of an increased elongation rate. Ni 2+ has no significant effect on the final plateau of actin polymerisation nor on the actin critical concentration. Electron microscopy revealed that actin filaments polymerised by 2 mM Ni 2+ showed some tendency to lateral aggregation, being frequently formed by the cohesion of two or three filaments. Furthermore, they often appeared shorter than those of control as also confirmed by the larger amount of free filament ends as well as the faster depolymerisation rate than control.
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