As estruturas CryoEM revelam como o flagelo bacteriano gira e muda de direção: mero acaso, fortuita necessidade ou design inteligente?

quinta-feira, julho 25, 2024

CryoEM structures reveal how the bacterial flagellum rotates and switches direction

Prashant K. Singh, Pankaj Sharma, Oshri Afanzar, Margo H. Goldfarb, Elena Maklashina, Michael Eisenbach, Gary Cecchini & T. M. Iverson 

Nature Microbiology volume 9, pages1271–1281 (2024)

Structure of the MS-ring


Abstract

Bacterial chemotaxis requires bidirectional flagellar rotation at different rates. Rotation is driven by a flagellar motor, which is a supercomplex containing multiple rings. Architectural uncertainty regarding the cytoplasmic C-ring, or ‘switch’, limits our understanding of how the motor transmits torque and direction to the flagellar rod. Here we report cryogenic electron microscopy structures for Salmonella enterica serovar typhimurium inner membrane MS-ring and C-ring in a counterclockwise pose (4.0 Å) and isolated C-ring in a clockwise pose alone (4.6 Å) and bound to a regulator (5.9 Å). Conformational differences between rotational poses include a 180° shift in FliF/FliG domains that rotates the outward-facing MotA/B binding site to inward facing. The regulator has specificity for the clockwise pose by bridging elements unique to this conformation. We used these structures to propose how the switch reverses rotation and transmits torque to the flagellum, which advances the understanding of bacterial chemotaxis and bidirectional motor rotation.

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