Numerous ATPases associated with diverse cellular activities (AAA+) proteins form hexameric, ring-shaped complexes that function via ATPase-coupled translocation of substrates across the central channel. Cryo-electron microscopy of AAA+ proteins processing substrate has revealed non-symmetric, staircase-like hexameric structures that indicate a sequential clockwise/2-residue step translocation model for these motors. However, for many of the AAA+ proteins that share similar structural features, their translocation properties have not yet been experimentally determined. In the cases where translocation mechanisms have been determined, a two-residue translocation step-size has not been resolved. In this review, we explore Hsp104, ClpB, ClpA and ClpX as examples to review the experimental methods that have been used to examine, in solution, the translocation mechanisms employed by AAA+ motor proteins. We then ask whether AAA+ motors sharing similar structural features can have different translocation mechanisms. Finally, we discuss whether a single AAA+ motor can adopt multiple translocation mechanisms that are responsive to different challenges imposed by the substrate or the environment. We suggest that AAA+ motors adopt more than one translocation mechanism and are tuned to switch to the most energetically efficient mechanism when constraints are applied.
The flower represents the Drosophila testis niche with the hub cells at the center. Each petal of the flower represents Germline stem cells (GSCs) with a large and a smaller purple circle representing centromere; green rays representing stronger centromeres preferentially attach to the niche. Red and green caterpillars represent sister chromatids in prometaphase with separable old and new H3 in GSCs. Further, large butterflies closer to the flower represent prometaphase GSCs with a red wing vs a green wing representing non-overlapping old and new H3. Small orange butterflies away from the flower represent prophase gonialblast cells with overlapping old and new H3 signals. The background is from coiled sperm from the fly testis. Cover art generated by Professor Tim Phelps.
AAA+ proteins: one motor, multiple ways to work
JiaBei Lin, James Shorter, Aaron L. Lucius; AAA+ proteins: one motor, multiple ways to work. Biochem Soc Trans 29 April 2022; 50 (2): 895–906. doi: https://doi.org/10.1042/BST20200350
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