Structural and catalytic properties and homology modelling of the human nucleoside diphosphate kinase C, product of the DRnm23 gene

The human DRnm23 gene was identified by differential screening of a cDNA li brary obtained from chronic myeloid leukaemia-blast crisis primary cells. T he over-expression of this gene inhibits differentiation and induces the ap optosis of myeloid precursor cell lines. We overproduced in bacteria a trun cated form of the encoded protein lacking the first 17 N-terminal amino aci ds. This truncated protein was called nucleoside diphosphate (NDP) kinase C Delta. NDP kinase Ca had similar kinetic properties to the major human NDP kinases A and B, but was significantly more stable to denaturation by urea and heat. Analysis of denaturation by urea, using size exclusion chromatog raphy, indicated unfolding without the dissociation of subunits, whereas re naturation occurred via a folded monomer. The stability of the protein depe nded primarily on subunit interactions. Homology modelling of the structure of NDP kinase C Delta, based on the crystal structure of NDP kinase B, ind icated that NDP kinase C Delta had several additional stabilizing interacti ons. The overall structure of the two enzymes appears to be identical becau se NDP kinase C Delta readily formed mixed hexamers with NDP kinase A. It i s possible that mixed hexamers can be observed in vivo.