1. The Alternating Power Stroke of a 6-Cylinder AAA Protease Chaperone Engine 
Wolfgang Kress, Eilika Weber-Ban 
Molecular Cell 
Volume 35, Issue 5, Pages (September 2009)
DOI: /j.molcel
Copyright © 2009 Elsevier Inc. Terms and Conditions

2. Figure 1
Intersubunit Signaling within the m-AAA Protease Results in Alternating Power Strokes Translocating the Substrate through the Central Pore
(A) In the ATP-bound state Yta12 (green) inhibits ATP hydrolysis in the adjacent Yta10 subunit (red). The R-finger motif is positioned by the presence of the γ-phosphate of ATP (yellow), such that the second R of the finger motif can make a salt bridge with an aspartate (D) at the end of helix 7 (α7). Helix 7 transmits the rearrangement to the Yta10 Walker B motif (E, catalytic glutamate) through pore loop-2.
(B) Two possible models for alternating power strokes in the m-AAA-ring. In both models the substrate interacts with pore loops of the active subunits (green), and substrate handover to the suppressed (subsequently becoming active) subunit (red) is triggered by ATP hydrolysis. This mechanism ensures that the AAA pore keeps a grip on the substrate at all times, similar to the way one would use one hand after the other (instead of both hands at the same time) to lift a weight using a pulley. In the upper panel, a hexamer consists of three active subunits (green) in the ATP-bound state making contact with the substrate at a time. The other three subunits are suppressed (red) but become active upon ATP hydrolysis and take over the substrate. In the lower panel, two opposing subunits are in the ATP-bound, active state (green) and inhibit the neighboring subunit (red). ATP hydrolysis induces the active state of the following protomer resulting in a stepwise transfer of ATPase activity along the ring. Considering that AAA-ATPases might not bind nucleotide to all six sites, the latter model seems more likely.
Molecular Cell  , DOI: ( /j.molcel )
Copyright © 2009 Elsevier Inc. Terms and Conditions