Direction determination in the minus-end-directed kinesin motor ncd

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Kinesin superfamily motor proteins transport intracellular cargo along microtubules.
• Different kinesins exhibit opposite directional motility (plus-end vs. minus-end) despite conserved catalytic cores.
• The structural basis for this directional difference remains unknown.

Purpose of the Study:

• To elucidate the structural basis for the opposite directional movement of kinesin superfamily motor proteins.
• To investigate the role of the 'neck' region in determining motor protein directionality.

Main Methods:

• Site-directed mutagenesis of the ncd (a minus-end-directed motor) neck region.
• Determination of the crystal structure of a functional ncd dimer at 2.5 Å resolution.
• Structural comparison of ncd and conventional kinesin (a plus-end-directed motor) neck regions.

Main Results:

• Mutagenesis of 13 class-specific residues in the ncd neck reversed its minus-end motility to plus-end.
• The ncd neck forms a coiled-coil structure, distinct from the interrupted beta-strand of the kinesin neck.
• Distinct neck architectures result in different dimer symmetries and directional bias on microtubules.

Conclusions:

• The ncd neck region is essential for minus-end-directed motility.
• Differences in neck structure, not the catalytic core, dictate the direction of kinesin motor proteins.
• Neck region architecture influences motor protein interaction with microtubules, conferring directional bias.