The Kinesin-14 tail: Dual microtubule binding domains drive spindle morphogenesis through tight microtubule...

Area of Science:

• Cell Biology
• Molecular Motors
• Cytoskeleton Dynamics

Background:

• Kinesin-14 (K-14) motors are crucial for organizing microtubules into the bipolar spindle.
• K-14 motors utilize motor and tail domains for cross-linking and sliding microtubules.
• The precise mechanisms by which K-14 motors mediate these diverse functions remain incompletely understood.

Purpose of the Study:

• To elucidate the distinct roles of microtubule-binding domains (MBD1 and MBD2) within the Xenopus K-14 XCTK2 tail.
• To investigate how these domains contribute to microtubule organization and spindle assembly.
• To characterize the differential effects of MBD mutations on microtubule cross-linking and sliding activities.

Main Methods:

• Identification and mutation of two microtubule-binding domains (MBD1 and MBD2) in the XCTK2 tail.
• Expression and localization analysis of wild-type and mutant GFP-XCTK2 proteins in Xenopus.
• Biochemical reconstitution assays to assess microtubule cross-linking and sliding velocities.

Main Results:

• Mutations in MBD1 (GX-MBD1^mut) and MBD2 (GX-MBD2^mut) differentially affected spindle assembly and microtubule organization.
• GX-MBD1^mut showed moderate spindle localization and narrow spindle formation, while GX-MBD2^mut exhibited weak localization and shorter spindles.
• Biochemical assays revealed that GX-MBD2^mut enhanced antiparallel microtubule sliding, whereas both GX-WT and GX-MBD1^mut primarily cross-linked parallel microtubules.

Conclusions:

• The two MBDs in K-14 tails balance antiparallel microtubule sliding (MBD1) and parallel microtubule cross-linking (MBD2) for effective spindle assembly.
• This differential domain function is critical for proper spindle organization, localization, and overall spindle assembly.
• Findings provide a mechanistic basis for understanding how molecular motors organize microtubules within the spindle apparatus.