MOLECULAR-BASIS OF A HEREDITARY TYPE-I PROTEIN-S DEFICIENCY CAUSED BYA SUBSTITUTION OF CYS FOR ARG474

The molecular basis for a hereditary type I protein S (PS) deficiency was investigated. DNA sequence analysis in the proband showed a novel missense mutation substituting Cys (TGT) for Arg474 (CGT) that is a hi ghly conserved amino acid residue among the related proteins. This mis sense mutation cosegregated with the type I PS deficiency in this fami ly. Transient expression studies showed that the secretion of the reco mbinant Cys-mutant PS was markedly decreased compared with that of the recombinant wild-type PS, reproducing the observed phenotype of type I deficiency. Stable expression and pulse-chase experiments demonstrat ed an intracellular degradation and an impaired secretion of the recom binant Cys-mutant PS. Furthermore, the substitution of Arg474 by Ala o r Glu, but not by Lys, markedly reduced the secretion of the recombina nt PS mutants in transient expression studies, suggesting that a posit ively charged basic amino acid might be needed at residue 474 and migh t play a key role in the protein structure and conformation of the sex hormone binding globulin-homology domain of the PS molecule. We postu late that the loss of the highly conserved Arg474 might be responsible for the type I PS deficiency inherited in this family. (C) 1996 by Th e American Society of Hematology.