Moreover, like the Killer-of-prune mutation in Drosophila NDK and the neuroblastoma Ser120 --> Gly mutation in human NDK-A/Nm23-H1, the Ser122 --> Pro substitution in NDK-B affects the stability of the protein toward heat and urea.
MDA-MB-435 human breast carcinoma cells were transfected with a control expression vector (pCMVBamneo), the vector containing the wild type nm23-H1, or the nm23-H1 vector encoding mutations at the following amino acids: serine 44, a phosphorylation site; proline 96, the k-pn mutation in the Drosophila nm23 homolog that causes developmental defects; histidine 118, involved in Nm23's nucleoside diphosphate kinase activity; and serine 120, a site of mutation in human neuroblastomas and phosphorylation.