PknD is a mycobacterial transmembrane protein with a cytosolic kinase domain and an extracellular sensor domain that contains NHL repeats. It plays a key role in the development of central nervous system tuberculosis, by mediating the invasion of host brain endothelia. The NHL (NCL-1, HT2A and LIN-41) repeat is found in multiple tandem copies, typically as 6 instances. It is about 40 residues long and resembles the WD repeat and other beta-propeller structures.