Residues in an ATP binding domain influence sugar binding in a trypanosome hexokinase

Trypanosoma brucei harbors two hexokinases (TbHK1 and TbHK2) that are 98% identical at the amino acid level. We previously found that recombinant TbHK1 (rTbHK1) has hexokinase activity, while rTbHK2 has not, a finding attributed to differences in the C-termini of the proteins. Sequence analysis suggests that the C-termini of TbHKs are part of a newly identified conserved motif found in other eukaryotic hexokinases. Here, we have explored the role of tail residues in the differences in catalytic activity between TbHK1 and TbHK2. Our studies reveal that tail residues D454, F462, M466, and N469 are essential for HK activity while both I458 and V468 are required for catalysis and substrate specificity. To activate rTbHK2, all of the residues important for activity in rTbHK1 (D454, V458, F462, M466, V468, and N469) were required. These results indicate that the overall structure of the C-terminal tail influences the HK activity of rTbHK1.