Unusual features and localization of the membrane kinome of Trypanosoma brucei

Abstract

In many eukaryotes, multiple protein kinases are situated in the plasma membrane where they respond to extracellular ligands. Ligand binding elicits a signal that is transmitted across the membrane, leading to activation of the cytosolic kinase domain. Humans have over 100 receptor protein kinases. In contrast, our search of the Trypanosoma brucei kinome showed that there were only ten protein kinases with predicted transmembrane domains, and unlike other eukaryotic transmembrane kinases, seven are predicted to bear multiple transmembrane domains. Most of the ten kinases, including their transmembrane domains, are conserved in both Trypanosoma cruzi and Leishmania species. Several possess accessory domains, such as Kelch, nucleotide cyclase, and forkhead-associated domains. Surprisingly, two contain multiple regions with predicted structural similarity to domains in bacterial signaling proteins. A few of the protein kinases have previously been localized to subcellular structures such as endosomes or lipid bodies. We examined the localization of epitope-tagged versions of seven of the predicted transmembrane kinases in T. brucei bloodstream forms and show that five localized to the endoplasmic reticulum. The last two kinases are enzymatically active, integral membrane proteins associated with the flagellum, flagellar pocket, or adjacent structures as shown by both fluorescence and immunoelectron microscopy. Thus, these kinases are positioned in structures suggesting participation in signal transduction from the external environment.

An essential Trypanosoma brucei protein kinase: a functional analysis of regulation and the identification of inhibitors

“…Subsequently, 500 µL of ice-cold methanol was added to the coverslips and the cells were incubated for an additional 30 min. The incubation and washing steps for antibody staining were as described in Jensen et al (2021). The antibodies used were mouse anti-V5 at 5.5 mg/mL, the glycosomal marker rabbit anti-PGK at 1 : 300, and the acidocalcisome marker rabbit anti-vacuolar pyrophosphatase at 1 : 400 (kindly gifted by Roberto Docampo).…”