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

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

Grenoble

Congreso; Congrès de la Société Française de Biochimie et Biologie Moléculaire (SFBBM)) et la Société Française de Biophysique (SFB); 2012

Société Française de Biochimie et Biologie Moléculaire (SFBBM)) et la Société Française de Biophysique (SFB)

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 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-γ 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.