Some time ago I posted breaking news about solved structure of usher pore. And few days ago it was deposited into PDB as 2VQI (publication appeared in Cell, here’s the abstract). The structure is a beatiful dimer (see above) of 24 stranded beta-barrel, the first of its kind. The paper contains also structures of the whole complex reconstructed based on cryo-EM data.
Interestingly, while the structure of the native dimer is symmetrical, the function of the units is not. Both of twinned pores are involved in alternating recruitment of chaperone:pili-subunit complexes, but only one actually transports pili subunits out. Overall, given large amount of detailed studies on the mechanistic properties of pili transport and formation, this is the best understood translocation process at a structural level.
Read the paper and draw your own conclusions, but for me it changes the way of thinking about protein translocation in bacteria. We learnt a lot on bacterial secretion by observing how similar proteins are involved in fundamentally different processes (for example DNA export and toxin secretion may use the same system). Similarly, usher pore is going to serve as an exemplar for newly found translocation elements.