Recurrence of carbamoyl phosphate synthetase 1 (CPS1) deficiency in Turkish patients: Characterization of a founder mutation by use of recombinant CPS1 from insect cells expression

WOS: 000346623000006PubMed ID: 25410056Carbamoyl phosphate synthetase 1 (CPS1) deficiency due to CPS1 mutations is a rare autosomal-recessive urea cycle disorder causing hyperammonemia that can lead to death or severe neurological impairment. CPS1 catalyzes carbamoyl phosphate formation from ammonia, bicarbonate and two molecules of ATP, and requires the allosteric activator N-acetyl-L-glutamate. Clinical mutations occur in the entire CPS1 coding region, but mainly in single families, with little recurrence. We characterized here the only currently known recurrent CPS1 mutation, p.Val1013del, found in eleven unrelated patients of Turkish descent using recombinant His-tagged wild type or mutant CPS1 expressed in baculovirus/insect cell system. The global CPS1 reaction and the ATPase and ATP synthesis partial reactions that reflect, respectively, the bicarbonate and the carbamate phosphorylation steps, were assayed. We found that CPS1 wild type and V1013del mutant showed comparable expression levels and purity but the mutant CPS1 exhibited no significant residual activities. In the CPS1 structural model, V1013 belongs to a highly hydrophobic beta-strand at the middle of the central beta-sheet of the A subdomain of the carbamate phosphorylation domain and is close to the predicted carbamate tunnel that links both phosphorylation sites. Haplotype studies suggested that p.Val1013del is a founder mutation. In conclusion, the mutation p.V1013del inactivates CPS1 but does not render the enzyme grossly unstable or insoluble. Recurrence of this particular mutation in Turkish patients is likely due to a founder effect, which is consistent with the frequent consanguinity observed in the affected population. (C) 2014 Elsevier Inc All rights reserved.Swiss National Science FoundationSwiss National Science Foundation (SNSF) [310030_127184, 310030_153196]; Ciberned-ISCIIIInstituto de Salud Carlos III [CB06-05-1123/Group 209]; Spanish GovernmentSpanish Government [BFU2011-30407, BFU 2011-30407]; Prometeo (Valencian Government) [II/2014/029]; Alicia Koplowitz FoundationWe thank Drs. D.S. Froese and P. Fully (Zurich, Switzerland) for the technical assistance and helpful suggestions by DSF experiments, and Dr. J.B. Hennermann, Dr. R. Santer for providing the patients' information. Mutation analysis in the patients was kindly supported by Orphan Europe, who had however no influence on planning of this study or writing of the manuscript. This work was supported by the Swiss National Science Foundation (grants 310030_127184 and 310030_153196 to J.H.). Work at JP-T laboratory was supported by Ciberned-ISCIII (CB06-05-1123/Group 209). V. Rubio was supported by grants BFU2011-30407 (Spanish Government, BFU 2011-30407), Prometeo (Valencian Government, II/2014/029) and from the Alicia Koplowitz Foundation (Conv. 2011/Encefalopatia)