Molecular motors move directionally to either the plus or the minus end
of microtubules or actin filaments. Kinesin moves towards microtubule plus
ends, whereas the kinesin-related Ncd motor moves to ...the minus ends. The 'neck'-the
region between the stalk and motor domain-is required for Ncd to move
to microtubule minus ends, but the mechanism underlying
directional motor movement is not understood. Here we show that a single amino-acid
change in the Ncd neck causes the motor to reverse directions and move with
wild-type velocities towards the plus or minus end; thus, the neck is functional
but directionality is defective. Mutation of a motor-core residue that touches
the neck residue in crystal structures also results in movement
in both directions, indicating that directed movement to the minus end requires
interactions of the neck and motor core. Low-density laser-trap assays show
that a conformational change or working stroke of the Ncd motor is directional
and biased towards the minus end, whereas that of the neck mutant occurs in
either direction. We conclude that the directional bias of the working stroke
is dependent on neck/motor core interactions. Absence of these interactions
removes directional constraints and permits movement in either direction.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
2.
Determinants of Kinesin Motor Polarity Endow, Sharyn A.; Waligora, Kimberly W.
Science (American Association for the Advancement of Science),
08/1998, Letnik:
281, Številka:
5380
Journal Article
Recenzirano
The kinesin motor protein family members move along microtubules with characteristic polarity. Chimeric motors containing the stalk and neck of the minus-end-directed motor, Ncd, fused to the motor ...domain of plus-end-directed kinesin were analyzed. The Ncd stalk and neck reversed kinesin motor polarity, but mutation of the Ncd neck reverted the chimeric motor to plus-end movement. Thus, residues or regions contributing to motor polarity must be present in both the Ncd neck and the kinesin motor core. The neck-motor junction was critical for Ncd minus-end movement; attachment of the neck to the stalk may also play a role.
A Standardized Kinesin Nomenclature Lawrence, Carolyn J.; Dawe, R. Kelly; Christie, Karen R. ...
The Journal of cell biology,
10/2004, Letnik:
167, Številka:
1
Journal Article
Recenzirano
Odprti dostop
In recent years the kinesin superfamily has become so large that several different naming schemes have emerged, leading to confusion and miscommunication. Here, we set forth a standardized kinesin ...nomenclature based on 14 family designations. The scheme unifies all previous phylogenies and nomenclature proposals, while allowing individual sequence names to remain the same, and for expansion to occur as new sequences are discovered.
Work over the past two years has led to a breakthrough in our understanding of the molecular basis of the directionality of the kinesin motor proteins. This breakthrough has come first from the ...reversal of directionality of the kinesin-related motor Ncd, followed closely by the reversal of kinesin's directionality and the finding that the Ncd 'neck' can convert Ncd or kinesin, which are intrinsically plus-end-directed microtubule motors, into a minus-end motor. These findings raise several outstanding questions, foremost, how does the neck function in motor directionality?
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Oocyte meiotic spindles of many species are anastral and lack centrosomes to nucleate microtubules. Assembly of anastral spindles occurs by a pathway that differs from that of most mitotic spindles. ...Here we analyze assembly of the Drosophila oocyte meiosis I spindle and the role of the Nonclaret disjunctional (Ncd) motor in spindle assembly using wild-type and mutant Ncd fused to GFP. Unexpectedly, we observe motor-associated asters at germinal vesicle breakdown that migrate towards the condensed chromosomes, where they nucleate microtubules at the chromosomes. Newly nucleated microtubules are randomly oriented, then become organized around the bivalent chromosomes. We show that the meiotic spindle forms by lateral associations of microtubule-coated chromosomes into a bipolar spindle. Lateral interactions between microtubule-associated bivalent chromosomes may be mediated by microtubule crosslinking by the Ncd motor, based on analysis of fixed oocytes. We report here that spindle assembly occurs in an ncd mutant defective for microtubule motility, but lateral interactions between microtubule-coated chromosomes are unstable, indicating that Ncd movement along microtubules is needed to stabilize interactions between chromosomes. A more severe ncd mutant that probably lacks ATPase activity prevents formation of lateral interactions between chromosomes and causes defective microtubule elongation. Anastral Drosophila oocyte meiosis I spindle assembly thus involves motor-associated asters to nucleate microtubules and Ncd motor activity to form and stabilize interactions between microtubule-associated chromosomes during the assembly process. This is the first complete account of assembly of an anastral spindle and the specific steps that require Ncd motor activity, revealing new and unexpected features of the process.
A new kinesin tree Dagenbach, Elise M; Endow, Sharyn A
Journal of cell science,
2004-Jan-01, 2004-01-01, 20040101, Letnik:
117, Številka:
Pt 1
Journal Article
Many of the kinesin microtubule motor proteins discovered during the past 8–9 years have roles in spindle assembly and function or chromosome movement during meiosis or mitosis. The discovery of ...kinesin motor proteins with a clear involvement in spindle and chromosome motility, together with recent evidence that cytoplasmic dynein plays a role in chromosome distribution, has attracted great interest. The identification of microtubule motors that function in chromosome distribution represents a major advance in understanding the forces that underlie chromosome and spindle movements during cell division.
AtKCBP is a calcium-dependent calmodulin-binding protein from Arabidopsis that contains a conserved kinesin microtubule motor domain. Calmodulin has been shown previously to bind to heavy chains of ...the unconventional myosins, where it is required for in vitro motility of brush border myosin I, but AtKCBP is the first kinesin-related heavy chain reported to be capable of binding specifically to calmodulin. Other kinesin proteins have been identified in Arabidopsis, but none of these binds to calmodulin, and none has been demonstrated to be a microtubule motor. We have tested bacterially expressed AtKCBP for the ability to bind microtubules to a glass surface and induce gliding of microtubules across the glass surface. We find that AtKCBP is a microtubule motor protein that moves on microtubules toward the minus ends, with the opposite polarity as kinesin. In the presence of calcium and calmodulin, AtKCBP no longer binds microtubules to the coverslip surface. This contrasts strikingly with the requirement of calmodulin for in vitro motility of brush border myosin I. Calmodulin could regulate AtKCBP binding to microtubules in the cell by inhibiting the binding of the motor to microtubules. The ability to bind to calmodulin provides an evolutionary link between the kinesin and myosin motor proteins, but our results indicate that the mechanisms of interaction and regulation of kinesin and myosin heavy chains by calmodulin are likely to differ significantly
A product encoded at the claret locus in Drosophila is needed for normal chromosome segregation in meiosis in females and in early mitotic divisions of the embryo. The predicted amino-acid sequence ...of the segregation protein was shown recently to be strikingly similar to Drosophila kinesin heavy chain. We have expressed the claret segregation protein in bacteria and have found that the bacterially expressed protein has motor activity in vitro with several novel features. The claret motor is slow (4 microns min-1), unlike either kinesin or dyneins. It has the directionality, the ability to generate torque and the sensitivity to inhibitors reported previously for dyneins. The finding of minus-end directed motor activity for a protein with sequence similarity to kinesin suggests that the dynein and kinesin motor domains are ancestrally related. The minus-end directed motor activity of the claret motor is consistent with a role for this protein in producing chromosome movement along spindle microtubules during prometaphase and/or anaphase.
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