Protein phosphorylation corrects the folding defect of the neuroblastoma (S120G) mutant of human nucleoside diphosphate kinase A/Nm23-H1.
Human nucleoside diphosphate (NDP) kinase A is a 'house-keeping' enzyme essential for the synthesis of nonadenine nucleoside (and deoxynucleoside) 5'-triphosphate. It is involved in complex cellular regulatory functions including the control of metastatic tumour dissemination. The mutation S120G has been identified in high-grade neuroblastomas. We have shown previously that this mutant has a folding defect: the urea-denatured protein could not refold in vitro. A molten globule folding intermediate accumulated, whereas the wild-type protein folded and associated into active hexamers. In the present study, we report that autophosphorylation of the protein corrected the folding defect. The phosphorylated S120G mutant NDP kinase, either autophosphorylated with ATP as donor, or chemically prosphorylated by phosphoramidate, refolded and associated quickly with high yield. Nucleotide binding had only a small effect. ADP and the non-hydrolysable ATP analogue 5'-adenyly-limido-diphosphate did not promote refolding. ATP-promoted refolding was strongly inhibited by ADP, indicating protein dephosphorylation. Our findings explain why the mutant enzyme is produced in mammalian cells and in Escherichia coli in a soluble form and is active, despite the folding defect of the S120G mutant observed in vitro. We generated an inactive mutant kinase by replacing the essential active-site histidine residue at position 118 with an asparagine residue, which abrogates the autophosphorylation. The double mutant H118N/S120G was expressed in inclusion bodies in E. coli. Its renaturation stops at a folding intermediate and cannot be reactivated by ATP in vitro. The transfection of cells with this double mutant might be a good model to study the cellular effects of folding intermediates.
Mocan
Iulia
I
Institut de Biochimie et Génétique Cellulaires (UMR 5095), Université Victor Segalen Bordeaux2 and CNRS, 33077 Bordeaux Cedex, France.
Georgescauld
Florian
F
Gonin
Philippe
P
Thoraval
Didier
D
Cervoni
Laura
L
Giartosio
Anna
A
Dabernat-Arnaud
Sandrine
S
Crouzet
Marc
M
Lacombe
Marie-Lise
ML
Lascu
Ioan
I
D000255:Adenosine Triphosphate / Q000378:metabolism; D019943:Amino Acid Substitution; D002384:Catalysis; D045744:Cell Line, Tumor; D017931:DNA Primers; D004789:Enzyme Activation; D006801:Humans; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D054778:NM23 Nucleoside Diphosphate Kinases; D009363:Neoplasm Proteins / Q000378:metabolism*; D009447:Neuroblastoma; D009701:Nucleoside-Diphosphate Kinase / Q000235:genetics* / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000378:metabolism
D017931:DNA Primers; D054778:NM23 Nucleoside Diphosphate Kinases; D009363:Neoplasm Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; C517938:NME1 protein, human; D009701:Nucleoside-Diphosphate Kinase