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FtsZ Protofilaments Use a Hinge-Opening Mechanism for Constrictive Force Generation

Science  26 Jul 2013:
Vol. 341, Issue 6144, pp. 392-395
DOI: 10.1126/science.1239248

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In a FtsZ

FtsZ is a guanosine triphosphatase that polymerizes into protofilaments at the bacterial division site. FtsZ recruits the accessory division proteins to the septum and also provides mechanical forces needed to constrict the membrane and reduce the cell width. However, how FtsZ generates mechanical force is unclear. While one popular model suggests that mechanical forces are generated by means of a change in FtsZ structure induced by guanosine triphosphate hydrolysis, nucleotide-dependent conformational transitions have yet to be observed in FtsZ monomer structures. Such transitions may be a feature of FtsZ only in its native protofilament-forming state. Li et al. (p. 392) sought to resolve this question by obtaining high-resolution structures of guanosine diphosphate–bound FtsZ filaments. The results suggest a complex and dynamic FtsZ protofilament network with a high degree of plasticity that is capable of generating forces to drive cytokinesis, during cycles of hydrolysis, while maintaining the structural integrity of individual monomers.

Abstract

The essential bacterial protein FtsZ is a guanosine triphosphatase that self-assembles into a structure at the division site termed the “Z ring”. During cytokinesis, the Z ring exerts a constrictive force on the membrane by using the chemical energy of guanosine triphosphate hydrolysis. However, the structural basis of this constriction remains unresolved. Here, we present the crystal structure of a guanosine diphosphate–bound Mycobacterium tuberculosis FtsZ protofilament, which exhibits a curved conformational state. The structure reveals a longitudinal interface that is important for function. The protofilament curvature highlights a hydrolysis-dependent conformational switch at the T3 loop that leads to longitudinal bending between subunits, which could generate sufficient force to drive cytokinesis.

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