Which, you will recall, is not supposed to be irreducibly complex:
More visuals here.
The paper is closed access but a friend swatched these graffs to us:
“Although the flagellum has been proposed to be the evolutionary ancestor of T3SSs, the structure of the flagellar motor is significantly different from that of the T3SS basal body (Figure S7I). The rod in the basal body of the Salmonella T3SS consists of two proteins, PrgJ and PrgI, and adopts a relatively simple helical structure. In contrast to the tight contacts of the T3SS rod with the secretin channel and the inner membrane ring, the flagellar rod has few contacts with the LP ring to facilitate its high-speed rotation and torque transmission. In addition, unlike the C24-symmetric inner membrane ring assembled by PrgH and PrgK in the Salmonella T3SS, the MS ring of the flagellar motor is composed of 34 FliF subunits with mixed internal symmetries. Therefore, the flagellar motor has evolved special structural elements for bacterial motility.
The flagellar motor is a rotary engine for torsional force transmission to enable bacterial motility. In contrast, the rotation of F/V-type ATPases, another type of natural rotational machinery (Kühlbrandt, 2019), transmits torque force to induce conformational changes of the enzymatic domain for ATP synthesis or hydrolysis. The torque transmission mechanism from the rotary ring structure to the axial rod in the flagellar motor (Figure S7J) is different from that utilized by F/V-ATPases, in which the membrane-bound rotary ring forms a perpendicular surface attachment with the central stalk via salt bridges for planar-to-axial torsional force transmission. Thus, this work presents the structural basis for assembly and torque transmission of the flagellar motor and indicates the diversity of torque transmission mechanisms of natural rotary protein machineries.” Jiaxing Tan, Xing Zhang, Xiaofei Wang, Caihuang Xu, Shenghai Chang, Hangjun Wu, Ting Wang, Huihui Liang, Haichun Gao, Yan Zhou, Yongqun Zhu, Structural basis of assembly and torque transmission of the bacterial flagellar motor, Cell, 2021, , ISSN 0092-8674, https://doi.org/10.1016/j.cell.2021.03.057.
As more of this type of information becomes available, expect the topic of irreducible complexity to be no longer discussable. When it can’t be debunked, it can be ruled undiscussable.