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Nucleotide-dependent structural changes in dimeric NCD molecules complexed to microtubules
K Hirose1, R A Cross, L A Amos
1National Institute for Advanced Interdisciplinary Research, Tsukuba 305, Japan.
Journal of Molecular Biology
|June 10, 1998
Summary
Motor proteins like kinesin-like protein ncd bind microtubules using one head, with the other tethered. Their structural changes during ATP turnover do not drive directional movement, suggesting dimer arrangement dictates directionality.
Area of Science:
- Molecular motor proteins
- Structural biology
- Cellular transport
Background:
- Kinesin-like protein ncd motors are crucial for intracellular transport.
- Understanding their nucleotide-bound states is key to elucidating motor function.
Purpose of the Study:
- To visualize and analyze different nucleotide-associated states of the ncd motor domain.
- To understand how these states influence motor-microtubule interactions and head positioning.
Main Methods:
- Cryoelectron microscopy
- Helical image reconstruction
- Analysis of dimeric ncd constructs (NDelta295-700) in ADP, AMP.PNP, and rigor states.
Main Results:
- Single-headed attachment to microtubules observed across all analyzed states.
- Differences in attached head-tubulin interaction and tethered head positioning were identified.
- The ATP-like (AMP.PNP) state showed the free head tilting towards the plus end.
Conclusions:
- Conformational changes in the bound head do not directly guide the free head's position.
- The relative orientation of ncd dimer heads is a primary determinant of motor directionality.
- Tethered heads consistently point towards the minus end, supporting the dimer arrangement hypothesis.