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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

The seesaw model for activation of kinesin by microtubules. a Schematic showing the correspondence of the crystal structure with elements in the seesaw cartoon. Selected side chain atoms are rendered with van der Waals spheres (fulcrum F82, Y84 are in gray), while the nucleotide is depicted by a ball-and-stick diagram. b Cartoon depiction of the seesaw. Positions of various structural elements are labeled. c Depiction of uncoupled seesaw motion in the absence of microtubules. Disordered neck linker is represented by a dashed magenta line; disordered loop L11 is represented by a dashed red line. While this panel depicts kinesin’s ADP state, the ATP state is expected to explore a similar set of conformations, in the absence of microtubules. d Depiction of microtubule-activated "seesaw" ATP sensing mechanism. The notch in the microtubule surface represents a conserved contact with residue N255 in the switch II helix. Grayed out bottom panels represent conformations disfavored by the seesaw coupling mechanism, so that a "pre-stroke" state is uniquely selected in the absence of ATP, and a "post-stroke" state is uniquely selected in the presence of ATP. Striped areas in the bottom panels represent unfavorable interactions generated either by (bottom left) steric overlap between I254 and the switch loops lining the nucleotide site or (bottom right) hydrophobic void formed by displacement of I254 out of the switch pocket
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Fig2: The seesaw model for activation of kinesin by microtubules. a Schematic showing the correspondence of the crystal structure with elements in the seesaw cartoon. Selected side chain atoms are rendered with van der Waals spheres (fulcrum F82, Y84 are in gray), while the nucleotide is depicted by a ball-and-stick diagram. b Cartoon depiction of the seesaw. Positions of various structural elements are labeled. c Depiction of uncoupled seesaw motion in the absence of microtubules. Disordered neck linker is represented by a dashed magenta line; disordered loop L11 is represented by a dashed red line. While this panel depicts kinesin’s ADP state, the ATP state is expected to explore a similar set of conformations, in the absence of microtubules. d Depiction of microtubule-activated "seesaw" ATP sensing mechanism. The notch in the microtubule surface represents a conserved contact with residue N255 in the switch II helix. Grayed out bottom panels represent conformations disfavored by the seesaw coupling mechanism, so that a "pre-stroke" state is uniquely selected in the absence of ATP, and a "post-stroke" state is uniquely selected in the presence of ATP. Striped areas in the bottom panels represent unfavorable interactions generated either by (bottom left) steric overlap between I254 and the switch loops lining the nucleotide site or (bottom right) hydrophobic void formed by displacement of I254 out of the switch pocket

Mentions: The atomic architecture of kinesin reveals that this motor possesses Walker-type nucleotide-sensing “switch” motifs common to a broad swath of ATPase and GTPase enzymes (Sablin et al. 1996). An important observation relating to the functioning of these motifs was that the switch II sensor loop is immediately N-terminal to the "switch II helix" that forms a major part of kinesin’s microtubule binding interface (see Table 1 and Fig. 2 for definitions of the switch regions and other key structural elements). Moreover, the switch II helix extends across the full width of the motor domain (Fig. 1f), reaching from the nucleotide cleft across to the opposite side where the C terminus of the catalytic domain emerges and (in conventional kinesins) attaches to cargo, via a putative force-generating element called the neck linker. This arrangement therefore suggested an elegant structural scheme for motor function whereby ATP binding in the motor would simultaneously modulate the microtubule binding affinity and also lead to cargo translocation, with both actions controlled via switch-loop-modulated changes in the geometry of the switch II helix (Kull et al. 1996; Sablin et al. 1996; Vale and Milligan 2000). Each of these of these putative functional roles for the switch II helix, modulation of microtubule attachment affinity and modulation of the conformation of the neck linker, constitutes a prediction which can be tested by structural and biophysical methods.Table 1


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

Sindelar CV - Biophys Rev (2011)

The seesaw model for activation of kinesin by microtubules. a Schematic showing the correspondence of the crystal structure with elements in the seesaw cartoon. Selected side chain atoms are rendered with van der Waals spheres (fulcrum F82, Y84 are in gray), while the nucleotide is depicted by a ball-and-stick diagram. b Cartoon depiction of the seesaw. Positions of various structural elements are labeled. c Depiction of uncoupled seesaw motion in the absence of microtubules. Disordered neck linker is represented by a dashed magenta line; disordered loop L11 is represented by a dashed red line. While this panel depicts kinesin’s ADP state, the ATP state is expected to explore a similar set of conformations, in the absence of microtubules. d Depiction of microtubule-activated "seesaw" ATP sensing mechanism. The notch in the microtubule surface represents a conserved contact with residue N255 in the switch II helix. Grayed out bottom panels represent conformations disfavored by the seesaw coupling mechanism, so that a "pre-stroke" state is uniquely selected in the absence of ATP, and a "post-stroke" state is uniquely selected in the presence of ATP. Striped areas in the bottom panels represent unfavorable interactions generated either by (bottom left) steric overlap between I254 and the switch loops lining the nucleotide site or (bottom right) hydrophobic void formed by displacement of I254 out of the switch pocket
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Related In: Results  -  Collection

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Fig2: The seesaw model for activation of kinesin by microtubules. a Schematic showing the correspondence of the crystal structure with elements in the seesaw cartoon. Selected side chain atoms are rendered with van der Waals spheres (fulcrum F82, Y84 are in gray), while the nucleotide is depicted by a ball-and-stick diagram. b Cartoon depiction of the seesaw. Positions of various structural elements are labeled. c Depiction of uncoupled seesaw motion in the absence of microtubules. Disordered neck linker is represented by a dashed magenta line; disordered loop L11 is represented by a dashed red line. While this panel depicts kinesin’s ADP state, the ATP state is expected to explore a similar set of conformations, in the absence of microtubules. d Depiction of microtubule-activated "seesaw" ATP sensing mechanism. The notch in the microtubule surface represents a conserved contact with residue N255 in the switch II helix. Grayed out bottom panels represent conformations disfavored by the seesaw coupling mechanism, so that a "pre-stroke" state is uniquely selected in the absence of ATP, and a "post-stroke" state is uniquely selected in the presence of ATP. Striped areas in the bottom panels represent unfavorable interactions generated either by (bottom left) steric overlap between I254 and the switch loops lining the nucleotide site or (bottom right) hydrophobic void formed by displacement of I254 out of the switch pocket
Mentions: The atomic architecture of kinesin reveals that this motor possesses Walker-type nucleotide-sensing “switch” motifs common to a broad swath of ATPase and GTPase enzymes (Sablin et al. 1996). An important observation relating to the functioning of these motifs was that the switch II sensor loop is immediately N-terminal to the "switch II helix" that forms a major part of kinesin’s microtubule binding interface (see Table 1 and Fig. 2 for definitions of the switch regions and other key structural elements). Moreover, the switch II helix extends across the full width of the motor domain (Fig. 1f), reaching from the nucleotide cleft across to the opposite side where the C terminus of the catalytic domain emerges and (in conventional kinesins) attaches to cargo, via a putative force-generating element called the neck linker. This arrangement therefore suggested an elegant structural scheme for motor function whereby ATP binding in the motor would simultaneously modulate the microtubule binding affinity and also lead to cargo translocation, with both actions controlled via switch-loop-modulated changes in the geometry of the switch II helix (Kull et al. 1996; Sablin et al. 1996; Vale and Milligan 2000). Each of these of these putative functional roles for the switch II helix, modulation of microtubule attachment affinity and modulation of the conformation of the neck linker, constitutes a prediction which can be tested by structural and biophysical methods.Table 1

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