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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.


Related in: MedlinePlus

Model for gating of ATP binding in the leading head, controlled by attachment of the trailing head. a Cartoon schematic indicating how the trailing head in a processively moving kinesin dimer generates rearwards strain on the neck linker that would “gate” ATP binding in the lead head. Rearwards strain prevents the neck linker/α6 assembly from binding into the hydrophobic docking pocket, thus leading to unfavorable energy if the seesaw tilts leftward to accommodate ATP binding (grayed out bottom panel). On the other hand, if the seesaw does not tilt in response to ATP binding, the switch loops cannot deform to interact with γ-phosphate without generating the switch pocket, which will be vacant (grayed out top panel). b Depiction of structure models showing the absence of support for a “twist-off” mechanism of gating between trailing and lead motor domains. Tilting caused by ATP binding in the forward head generates almost no displacement by the neck linker attachment point. Crystal structures were fitted into a composite density map, where the density for the trailing head is from an 8-Å resolution map of the ADP•Al•Fx state of kinesin-1 and density for the leading head is from the corresponding no-nucleotide map (Sindelar and Downing 2010). Axis of rotation identified for core domain movement during the transition from no-nucleotide to ADP•Al•Fx motor states is indicated by the green rod. c Comparison of predicted location of I325 at the α6/neck linker junction, before and after occupation of the docking pocket in the leading head by this residue accompanying neck linker docking. The resulting 5-Å displacement is consistent with a gating mechanism whereby rearwards strain prevents I325 from occupying the docking pocket
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Fig4: Model for gating of ATP binding in the leading head, controlled by attachment of the trailing head. a Cartoon schematic indicating how the trailing head in a processively moving kinesin dimer generates rearwards strain on the neck linker that would “gate” ATP binding in the lead head. Rearwards strain prevents the neck linker/α6 assembly from binding into the hydrophobic docking pocket, thus leading to unfavorable energy if the seesaw tilts leftward to accommodate ATP binding (grayed out bottom panel). On the other hand, if the seesaw does not tilt in response to ATP binding, the switch loops cannot deform to interact with γ-phosphate without generating the switch pocket, which will be vacant (grayed out top panel). b Depiction of structure models showing the absence of support for a “twist-off” mechanism of gating between trailing and lead motor domains. Tilting caused by ATP binding in the forward head generates almost no displacement by the neck linker attachment point. Crystal structures were fitted into a composite density map, where the density for the trailing head is from an 8-Å resolution map of the ADP•Al•Fx state of kinesin-1 and density for the leading head is from the corresponding no-nucleotide map (Sindelar and Downing 2010). Axis of rotation identified for core domain movement during the transition from no-nucleotide to ADP•Al•Fx motor states is indicated by the green rod. c Comparison of predicted location of I325 at the α6/neck linker junction, before and after occupation of the docking pocket in the leading head by this residue accompanying neck linker docking. The resulting 5-Å displacement is consistent with a gating mechanism whereby rearwards strain prevents I325 from occupying the docking pocket

Mentions: The seesaw scheme can account for such an "ATP gating" mechanism as follows (Fig. 4a). Strain generated by a strongly attached trailing head would prevent forward extension of the neck linker and accompanying occupation of the docking pocket by kinesin’s α6/neck linker assembly. Consequently, if the seesaw within the leading head were to assume the ATP-bound conformation having an open docking pocket, no compensating hydrophobic interactions could be made by the α6/neck linker assembly in this head. On the other hand, if the seesaw within leading head maintains a closed docking pocket, formation of the switch pocket on the opposite side of the seesaw (required for the switch loops to assume a strong hydrogen bond network with the γ-phosphate of ATP) will not be favored owing to displacement of I254 (located on the switch II helix extension) away from the seesaw interface. In this latter circumstance, switch pocket formation would create an unfavorable hydrophobic cavity on the left-hand side of the seesaw. Thus, if the lead head is under rearwards strain but simultaneously is bound to ATP, both leftwards as well as rightwards seesaw orientations in this head are disfavored by unoccupied hydrophobic cavities so that ATP binding itself would be disfavored. This mechanism thus provides a means by which the trailing head can gate ATP binding in the lead head.Fig. 4


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

Sindelar CV - Biophys Rev (2011)

Model for gating of ATP binding in the leading head, controlled by attachment of the trailing head. a Cartoon schematic indicating how the trailing head in a processively moving kinesin dimer generates rearwards strain on the neck linker that would “gate” ATP binding in the lead head. Rearwards strain prevents the neck linker/α6 assembly from binding into the hydrophobic docking pocket, thus leading to unfavorable energy if the seesaw tilts leftward to accommodate ATP binding (grayed out bottom panel). On the other hand, if the seesaw does not tilt in response to ATP binding, the switch loops cannot deform to interact with γ-phosphate without generating the switch pocket, which will be vacant (grayed out top panel). b Depiction of structure models showing the absence of support for a “twist-off” mechanism of gating between trailing and lead motor domains. Tilting caused by ATP binding in the forward head generates almost no displacement by the neck linker attachment point. Crystal structures were fitted into a composite density map, where the density for the trailing head is from an 8-Å resolution map of the ADP•Al•Fx state of kinesin-1 and density for the leading head is from the corresponding no-nucleotide map (Sindelar and Downing 2010). Axis of rotation identified for core domain movement during the transition from no-nucleotide to ADP•Al•Fx motor states is indicated by the green rod. c Comparison of predicted location of I325 at the α6/neck linker junction, before and after occupation of the docking pocket in the leading head by this residue accompanying neck linker docking. The resulting 5-Å displacement is consistent with a gating mechanism whereby rearwards strain prevents I325 from occupying the docking pocket
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Related In: Results  -  Collection

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Fig4: Model for gating of ATP binding in the leading head, controlled by attachment of the trailing head. a Cartoon schematic indicating how the trailing head in a processively moving kinesin dimer generates rearwards strain on the neck linker that would “gate” ATP binding in the lead head. Rearwards strain prevents the neck linker/α6 assembly from binding into the hydrophobic docking pocket, thus leading to unfavorable energy if the seesaw tilts leftward to accommodate ATP binding (grayed out bottom panel). On the other hand, if the seesaw does not tilt in response to ATP binding, the switch loops cannot deform to interact with γ-phosphate without generating the switch pocket, which will be vacant (grayed out top panel). b Depiction of structure models showing the absence of support for a “twist-off” mechanism of gating between trailing and lead motor domains. Tilting caused by ATP binding in the forward head generates almost no displacement by the neck linker attachment point. Crystal structures were fitted into a composite density map, where the density for the trailing head is from an 8-Å resolution map of the ADP•Al•Fx state of kinesin-1 and density for the leading head is from the corresponding no-nucleotide map (Sindelar and Downing 2010). Axis of rotation identified for core domain movement during the transition from no-nucleotide to ADP•Al•Fx motor states is indicated by the green rod. c Comparison of predicted location of I325 at the α6/neck linker junction, before and after occupation of the docking pocket in the leading head by this residue accompanying neck linker docking. The resulting 5-Å displacement is consistent with a gating mechanism whereby rearwards strain prevents I325 from occupying the docking pocket
Mentions: The seesaw scheme can account for such an "ATP gating" mechanism as follows (Fig. 4a). Strain generated by a strongly attached trailing head would prevent forward extension of the neck linker and accompanying occupation of the docking pocket by kinesin’s α6/neck linker assembly. Consequently, if the seesaw within the leading head were to assume the ATP-bound conformation having an open docking pocket, no compensating hydrophobic interactions could be made by the α6/neck linker assembly in this head. On the other hand, if the seesaw within leading head maintains a closed docking pocket, formation of the switch pocket on the opposite side of the seesaw (required for the switch loops to assume a strong hydrogen bond network with the γ-phosphate of ATP) will not be favored owing to displacement of I254 (located on the switch II helix extension) away from the seesaw interface. In this latter circumstance, switch pocket formation would create an unfavorable hydrophobic cavity on the left-hand side of the seesaw. Thus, if the lead head is under rearwards strain but simultaneously is bound to ATP, both leftwards as well as rightwards seesaw orientations in this head are disfavored by unoccupied hydrophobic cavities so that ATP binding itself would be disfavored. This mechanism thus provides a means by which the trailing head can gate ATP binding in the lead head.Fig. 4

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.


Related in: MedlinePlus