Mechanism of Directional Translocation Involves Target Search Coupled to Allosteric Motor Activation

CATTONI DIEGO; CHARA OSVALDO; GODEFROY C; MARGEAT E; TRIGUEROS SONIA; NÖLLMANN MARCELO

Philadelphia, Pennsylvania

Congreso; Biophysical Society 57th Annual Meeting; 2013

Biophysical Society

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-g/FtsK-g) and highly-skewed chromosomal sequences (SRS/KOPS). using a novel combination of bulk and single-molecule methods we dissect the series of steps required for SRS localization and motor activation. First, we demonstrate that SpoIIIE/DNA association kinetics are sequence-independent with binding specificity being uniquely determined by dissociation. Next, we show by 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-g to SRS triggering allosteric motor activation. 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.