Mitosis, or cell division, is the mechanism by which cells divide and is an intricate process requiring the action and control of numerous proteins. Such proteins serve either as structural entities within the mitotic spindle, or perform the "work" within the apparatus. In particular, Kinesin-5 motor proteins, a subset within the kinesin motor protein superfamily, are primarily responsible for organization of microtubules (MTs) within the mitotic apparatus, and are consequently vital for efficient mitosis. These proteins utilize energy from ATP hydrolysis in order to "walk" along antiparallel MTs, positioning them into the bipolar mitotic spindle. Loss of Kinesin-5 activity results in formation of a monoastral spindle and subsequent cell cycle arrest. Recently, a wide variety of small molecules have been identified that possess the ability to inhibit certain Kinesin-5 motors. Such compounds, including monastrol (the first Kinesin-5 inhibitor identified), have been employed to study Kinesin-5 activity. A thorough understanding of Kinesin-5 function, combined with the ability to specifically target these proteins with small molecules, may provide the capability to control cell division and may therefore have significant implications in anti-cancer therapies. The following dissertation describes research that utilizes small molecules to probe the function (ATPase activity and MT interactions) of various Kinesin-5 proteins and provides information that will lead to a better understanding of exactly how such proteins function in vivo. Further, a greater knowledge of Kinesin-5 protein activity as well as specific interactions with small-molecule compounds, may lead to the development of more potent, less toxic anti-cancer drugs. / Ph. D.

La kinésine mitotique humaine HsEg5 est essentielle à la division cellulaire. Ce moteur moléculaire permet la séparation des centrosomes et la mise en place du fuseau mitotique, structure nécessaire au partage équitable de l'information génétique. La suppression de la fonction d'HsEg5 bloque les cellules en pré-métaphase avec un fuseau mitotique monoastral caractéristique constitué des deux centrosomes non séparés entourés d'un anneau de chromosomes et de microtubules. Le maintien de ce phénotype peut conduire à la mort cellulaire programmée via l'activation du point de contrôle du fuseau mitotique (transition métaphase-anaphase). HsEg5 est ainsi considérée comme une cible anticancéreuse particulièrement intéressante. <br />Au cours de ces travaux, nous nous sommes intéressés aux interactions entre le domaine moteur d'HsEg5 et plusieurs inhibiteurs. Les zones d'interaction et de modifications conformationnelles ont été étudiées par échanges hydrogène/deutérium–spectrométrie de masse et mutagenèse dirigée. Cette approche expérimentale nous a permis d'identifier un « point chaud » d'inhibition sur le domaine moteur et de caractériser les mécanismes de deux inhibiteurs : le monastrol et le S-trityl-l-cystéine.