SpoIIIE mechanism of directional translocation involves target search coupled to allosteric motor activation.

CATTONI DIEGO; CHARA OSVALDO; GODEFROY CÉDRIC; MARGEAT E; TRIGUEROS SONIA; MILHIET PIERRE-EMMANUEL; NÖLLMANN MARCELO

Cambridge

Congreso; EMBO Conference - Helicases and Nucleic Acid Translocases; 2013

EMBO and the Harden Conferences

SpoIIIE/FtsK are membrane-anchored, ATP-fueled, directional motors responsible for chromosomal segregation in bacteria.Directionality in these motors is governed by interactions between specialized sequence-recognition modules (SpoIIIE-γ/FtsK-γ)and highly-skewed chromosomal sequences (SRS/KOPS). Using a novel combination of ensemble and single-molecule methodswe dissect the series of steps required for SRS localization and motor activation. First, we demonstrate that SpoIIIE/DNAassociation kinetics are sequence-independent with binding specificity being uniquely determined by dissociation. Next, we showby single-molecule and modeling methods that hexameric SpoIIIE binds DNA non-specifically and finds SRS by an ATP-independent target search mechanism, with ensuing oligomerization and binding of SpoIIIE-γ to SRS triggering motor stimulation.We propose a new model that provides an entirely novel interpretation of previous observations for the origin of SRS/KOPS-directed translocation by SpoIIIE/FtsK.