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Proteomic Analysis of the Mammalian Katanin Family of Microtubule‐severing Enzymes Defines KATNBL1 as a Regulator of Mammalian Katanin Microtubule‐severing

The Katanin family of microtubule‐severing enzymes are critical for remodeling microtubule‐based structures that influence cell division, motility, morphogenesis and signaling. In lower eukaryotes, Katanin is composed of a catalytic p60 subunit (A subunit, KATNA1) and a regulatory p80 subunit (B subunit, KATNB1). However, the mammalian genome encodes two additional A‐like subunits (KATNAL1 and KATNAL2) and one additional B‐like subunit (KATNBL1) that have remained poorly characterized. To better understand the factors and mechanisms controlling mammalian microtubule‐severing, we have taken a mass proteomic approach to define the protein interaction module for each mammalian Katanin subunit and to generate the mammalian Katanin family interaction network (Katan‐ome). Further, we have analyzed the function of the KATNBL1 subunit and determined that it associates with KATNA1 and KATNAL1, it localizes to the spindle poles only during mitosis and it regulates Katanin A subunit microtubule‐severing activity in vitro. Interestingly, during interphase, KATNBL1 is actively sequestered in the nucleus through an N‐terminal nuclear localization signal. Finally KATNB1 was able to compete the interaction of KATNBL1 with KATNA1 and KATNAL1. These data indicate that KATNBL1 functions as a regulator of Katanin A subunit microtubule‐severing activity during mitosis and that it likely coordinates with KATNB1 to perform this function.