Mutations affecting the beta-beta homomeric interaction in propionic acidaemia: an approach to the determination of the beta-propionyl-CoA carboxylase functional domains.

Abstract

Propionyl-CoA carboxylase (PCC; EC 6.4.1.3) deficiency in humans results in the autosomal recessive inherited disease propionic acidaemia (PA; McKusick 232000, 232050) (Fenton and Rosenberg 1995). This nuclear-encoded but mitochondrial enzyme has a biotin-dependent carboxylase activity and functions as a dodecameric complex of α and β subunits (α 6 β 6 ), which are encoded by the PCCA and PCCB genes. Knowledge of the human α-PCC and β-PCC cDNAs, as well as of the PCCB gene, has allowed an extensive analysis of the molecular basis of this metabolic disease. Several different mutant allele types affecting these loci in caucasian and oriental populations have been identified (Ugarte et al., 1999). On the basis of the polymeric nature of the enzyme PCC, we have studied the β-β homodimeric interaction using the in vivo mammalian two-hybrid system in COS cells. Here we report, for the first time, the existence of this interaction and the analysis of the effect of the PCCB gene mutations A497V, R512C, L519P and W531X on this dimeric association. This experimental approach appears to be a useful technique not only to highlight the β subunit oligomerization but also to analyse the effect of other mutant β-PCC proteins.