RT Journal Article
SR Electronic
T1 Polymer dynamics of Alp7A reveals two ‘critical’ concentrations that govern dynamically unstable actin-like proteins
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 098954
DO 10.1101/098954
A1 Natalie A. Petek
A1 Alan I. Derman
A1 Jason A. Royal
A1 Joe Pogliano
A1 R. Dyche Mullins
YR 2017
UL http://biorxiv.org/content/early/2017/01/10/098954.abstract
AB Dynamically unstable polymers capture and move cellular cargos in both bacteria and eukaryotes, but the regulation of their assembly remains poorly understood. Here we describe polymerization of Alp7A, a bacterial Actin-Like Protein (ALP) that segregates the low copy-number plasmid pLS20 in Bacillus subtilis. Purified Alp7A forms dynamically unstable polymers with two critical points: an intrinsic critical concentration (0.6 μM), observed when ATP hydrolysis is blocked, and a dynamic critical concentration (10.3 μM), observed when ATP hydrolysis occurs. From biochemical and kinetic analysis, the intrinsic critical concentration reflects a balance between filament elongation and shortening, while the dynamic critical concentration reflects a balance between filament nucleation and catastrophic disassembly. Although Alp7A does not form stable polymers at physiological concentrations, rapid nucleation by an accessory factor, Alp7R, decreases the dynamic critical concentration into the physiological range. Intrinsic and dynamic critical concentrations are fundamental parameters that can be used to describe the behavior of all dynamically unstable polymers.