Reversing a ‘backwards’ motor

Crystal structure of the motor domain of the human kinetochore protein CENP-E

The human kinetochore is a highly complex macromolecular structure that connects chromosomes to spindle microtubules (MTs) in order to facilitate accurate chromosome segregation. Centromere-associated protein E (CENP-E), a member of the kinesin superfamily, is an essential component of the kinetochore, since it is required to stabilize the attachment of chromosomes to spindle MTs, to develop tension across aligned chromosomes, to stabilize spindle poles and to satisfy the mitotic checkpoint. Here we report the 2.5A resolution crystal structure of the motor domain and linker region of human CENP-E with MgADP bound in the active site. This structure displays subtle but important differences compared to the structures of human Eg5 and conventional kinesin. Our structure reveals that the CENP-E linker region is in a "docked" position identical to that in the human plus-end directed conventional kinesin. CENP-E has many advantages as a potential anti-mitotic drug target and this crystal structure of human CENP-E will provide a starting point for high throughput virtual screening of potential inhibitors.

Determinants of molecular motor directionality

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?

Embryonic asymmetry: the left side gets all the best genes

The origin of left-right developmental asymmetry is a continuing puzzle, but some recent results provide new insights into the steps leading to organ asymmetry - implicating the homeobox protein Pitz-2 in one key step - and others support a model of symmetry-breaking that involves the chirality of microtubules.

Determinants of kinesin motor polarity

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.