Aspergillus fumigatus is a major pathogen of invasive pulmonary aspergillosis with high mortality rate. The nucleoside diphosphate kinase of A. fumigatus, AfNDK (also called SwoH) is essential for its viability, however, its structural characteristic was unknown. In this study, we solved the crystal structure of AfNDK and found that it exists predominantly in form of tetramer in solution. Oligomeric form rather than dimeric form was essential for its kinase activity. The Arg30 and the C terminal amino acids were crucial for dimer-dimer interaction and the viability of A. fumigatus. Mutation V83F might make the secondary structure alpha 5 helix protrude outward so that the whole protein structure became unstable at higher temperature, which might subsequently result to the inviability of A. fumigatus under 44 degrees C. In conclusion, the crystal structure of AfNDK was for the first time analyzed and the stability of the tetrameric form with dimer-dimer interaction were crucial for its function in A. fumigatus. (C) 2019 Elsevier Inc. All rights reserved.