Identification of CfNek, a novel member of the NIMA family of cell cycle regulators, as a polypeptide copurifying with tubulin polyglutamylation activity in Crithidia

Abstract

Post-translational glutamylation of tubulin plays an important role in regulating the interaction between microtubules and associated proteins, but so far the enzymes involved in this process have not been cloned from any cellular source. Using a modified purification scheme that employs a hydroxyapaptite chromatography as the final step we identified a 54 kDa band as the major polypeptide copurifying with tubulin polyglutamylation activity from the trypanosomatid Crithidia fasciculata. Based on peptide sequence information we have cloned the corresponding cDNA and identify Crithidia p54 as a novel member (termed CfNek) of the NIMA family of putative cell cycle regulators. CfNek is a protein of 479 amino acids that contains an unusual protein kinase domain that lacks the glycine-rich loop in subdomain I. The protein also harbours a PEST sequence and a pleckstrin homology domain. The tubulin polyglutamylase preparation displays theβ-casein phosphorylation activity typical for NIMA related kinases. Recombinant His-tagged CfNek expressed in Crithidia localises to the flagellar attachment zone/basal body of the parasite. After purification on a Ni2+-column the recombinant enzyme preparation displays ATP-dependent tubulin polyglutamylation activity as well as casein-phosphorylation activity.