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A seesaw model for intermolecular gating in the kinesin motor protein.

Sindelar CV - Biophys Rev (2011)

Bottom Line: Recent structural observations of kinesin-1, the founding member of the kinesin group of motor proteins, have led to substantial gains in our understanding of this molecular machine.The new structural information revises or replaces key details of earlier models of kinesin's ATPase cycle that were based principally on crystal structures of free kinesin, and demonstrates that high-resolution characterization of the kinesin-microtubule complex is essential for understanding the structural basis of the cycle.I discuss the broader implications of the seesaw mechanism within the cycle of a fully functional kinesin dimer and show how the seesaw can account for two types of "gating" that keep the ATPase cycles of the two heads out of sync during processive movement.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, SHMC-E25, 333 Cedar Street, New Haven, CT 06520-8024 USA.

ABSTRACT
Recent structural observations of kinesin-1, the founding member of the kinesin group of motor proteins, have led to substantial gains in our understanding of this molecular machine. Kinesin-1, similar to many kinesin family members, assembles to form homodimers that use alternating ATPase cycles of the catalytic motor domains, or "heads", to proceed unidirectionally along its partner filament (the microtubule) via a hand-over-hand mechanism. Cryo-electron microscopy has now revealed 8-Å resolution, 3D reconstructions of kinesin-1•microtubule complexes for all three of this motor's principal nucleotide-state intermediates (ADP-bound, no-nucleotide, and ATP analog), the first time filament co-complexes of any cytoskeletal motor have been visualized at this level of detail. These reconstructions comprehensively describe nucleotide-dependent changes in a monomeric head domain at the secondary structure level, and this information has been combined with atomic-resolution crystallography data to synthesize an atomic-level "seesaw" mechanism describing how microtubules activate kinesin's ATP-sensing machinery. The new structural information revises or replaces key details of earlier models of kinesin's ATPase cycle that were based principally on crystal structures of free kinesin, and demonstrates that high-resolution characterization of the kinesin-microtubule complex is essential for understanding the structural basis of the cycle. I discuss the broader implications of the seesaw mechanism within the cycle of a fully functional kinesin dimer and show how the seesaw can account for two types of "gating" that keep the ATPase cycles of the two heads out of sync during processive movement.

No MeSH data available.


Illustration of 8-Å resolution ADP and no-nucleotide density maps for microtubule-attached kinesin-1, showing a significant conformational change of the switch I loop (gold) and the P-loop (circled in blue) between these two nucleotide states: in the no-nucleotide state, the switch I loop intrudes into the nucleotide cleft accompanied by loss of ADP density and also loss of P-loop density. ADP is rendered as a ball-and-stick diagram
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Fig6: Illustration of 8-Å resolution ADP and no-nucleotide density maps for microtubule-attached kinesin-1, showing a significant conformational change of the switch I loop (gold) and the P-loop (circled in blue) between these two nucleotide states: in the no-nucleotide state, the switch I loop intrudes into the nucleotide cleft accompanied by loss of ADP density and also loss of P-loop density. ADP is rendered as a ball-and-stick diagram

Mentions: The cryo-EM maps of (Sindelar and Downing 2010) have since been refined from ∼9-Å to ∼8-Å resolution (C.V.S., unpublished data), and the corresponding increase in map quality further supports the interpretation that the nucleotide cleft is fully vacated under these experimental conditions (Fig. 6). Both no-nucleotide as well as ADP-bound motor states, as visualized in these EM maps, exhibit "ADP-like" orientations of the switch II helix. These observations indicate that "ADP-like" orientations of the switch II helix can occur in both tightly microtubule-attached (no-nucleotide) as well as weakly attached (ADP-bound) states of the motor. The conformation of the switch II helix itself also appears largely the same in these two maps; the density indicates that the helix maintains structure in its N-terminal "extension" coils (Sindelar and Downing 2010). Cryo-EM results with conventional kinesin are thus quite difficult to reconcile with any version of the ADP "twist-off" scheme. An alternative scheme, suggested by Minehardt et al. (2001), might be that microtubule attachment affects the switch I loop through a pathway involving the microtubule-binding loop L8, which connects to the switch I loop via the helix α3. A mutation in L8 is found to stall kinesin in a tightly attached ADP state following hydrolysis, which could lend support to this suggestion (Klumpp et al. 2003).Fig. 6


A seesaw model for intermolecular gating in the kinesin motor protein.

Sindelar CV - Biophys Rev (2011)

Illustration of 8-Å resolution ADP and no-nucleotide density maps for microtubule-attached kinesin-1, showing a significant conformational change of the switch I loop (gold) and the P-loop (circled in blue) between these two nucleotide states: in the no-nucleotide state, the switch I loop intrudes into the nucleotide cleft accompanied by loss of ADP density and also loss of P-loop density. ADP is rendered as a ball-and-stick diagram
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3117274&req=5

Fig6: Illustration of 8-Å resolution ADP and no-nucleotide density maps for microtubule-attached kinesin-1, showing a significant conformational change of the switch I loop (gold) and the P-loop (circled in blue) between these two nucleotide states: in the no-nucleotide state, the switch I loop intrudes into the nucleotide cleft accompanied by loss of ADP density and also loss of P-loop density. ADP is rendered as a ball-and-stick diagram
Mentions: The cryo-EM maps of (Sindelar and Downing 2010) have since been refined from ∼9-Å to ∼8-Å resolution (C.V.S., unpublished data), and the corresponding increase in map quality further supports the interpretation that the nucleotide cleft is fully vacated under these experimental conditions (Fig. 6). Both no-nucleotide as well as ADP-bound motor states, as visualized in these EM maps, exhibit "ADP-like" orientations of the switch II helix. These observations indicate that "ADP-like" orientations of the switch II helix can occur in both tightly microtubule-attached (no-nucleotide) as well as weakly attached (ADP-bound) states of the motor. The conformation of the switch II helix itself also appears largely the same in these two maps; the density indicates that the helix maintains structure in its N-terminal "extension" coils (Sindelar and Downing 2010). Cryo-EM results with conventional kinesin are thus quite difficult to reconcile with any version of the ADP "twist-off" scheme. An alternative scheme, suggested by Minehardt et al. (2001), might be that microtubule attachment affects the switch I loop through a pathway involving the microtubule-binding loop L8, which connects to the switch I loop via the helix α3. A mutation in L8 is found to stall kinesin in a tightly attached ADP state following hydrolysis, which could lend support to this suggestion (Klumpp et al. 2003).Fig. 6

Bottom Line: Recent structural observations of kinesin-1, the founding member of the kinesin group of motor proteins, have led to substantial gains in our understanding of this molecular machine.The new structural information revises or replaces key details of earlier models of kinesin's ATPase cycle that were based principally on crystal structures of free kinesin, and demonstrates that high-resolution characterization of the kinesin-microtubule complex is essential for understanding the structural basis of the cycle.I discuss the broader implications of the seesaw mechanism within the cycle of a fully functional kinesin dimer and show how the seesaw can account for two types of "gating" that keep the ATPase cycles of the two heads out of sync during processive movement.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, SHMC-E25, 333 Cedar Street, New Haven, CT 06520-8024 USA.

ABSTRACT
Recent structural observations of kinesin-1, the founding member of the kinesin group of motor proteins, have led to substantial gains in our understanding of this molecular machine. Kinesin-1, similar to many kinesin family members, assembles to form homodimers that use alternating ATPase cycles of the catalytic motor domains, or "heads", to proceed unidirectionally along its partner filament (the microtubule) via a hand-over-hand mechanism. Cryo-electron microscopy has now revealed 8-Å resolution, 3D reconstructions of kinesin-1•microtubule complexes for all three of this motor's principal nucleotide-state intermediates (ADP-bound, no-nucleotide, and ATP analog), the first time filament co-complexes of any cytoskeletal motor have been visualized at this level of detail. These reconstructions comprehensively describe nucleotide-dependent changes in a monomeric head domain at the secondary structure level, and this information has been combined with atomic-resolution crystallography data to synthesize an atomic-level "seesaw" mechanism describing how microtubules activate kinesin's ATP-sensing machinery. The new structural information revises or replaces key details of earlier models of kinesin's ATPase cycle that were based principally on crystal structures of free kinesin, and demonstrates that high-resolution characterization of the kinesin-microtubule complex is essential for understanding the structural basis of the cycle. I discuss the broader implications of the seesaw mechanism within the cycle of a fully functional kinesin dimer and show how the seesaw can account for two types of "gating" that keep the ATPase cycles of the two heads out of sync during processive movement.

No MeSH data available.