Propionic acidemia is an inherited metabolic disorder caused by deficiency of 
propionyl-CoA carboxylase, a dodecameric enzyme composed of alpha-PCC and 
beta-PCC subunits (encoded by genes PCCA and PCCB) that have been associated 
with a number of mutations responsible for this disease. To clarify the 
molecular effect associated with gene alterations causing propionic acidemia, 12 
different mutations affecting the PCCB gene (R67S, S106R, G131R, R165W, R165Q, 
E168K, G198D, A497V, R512C, L519P, W531X, and N536D) were analyzed for their 
involvement in alpha-beta heteromeric and beta-beta homomeric assembly. The 
experiments were performed using the mammalian two-hybrid system, which was 
assayed at two different temperatures to distinguish between mutations directly 
involved in interaction and those probably affecting polypeptide folding, thus 
indirectly affecting the correct assembly. Mutations R512C, L519P, W531X, and 
N536D, located at the carboxyl-terminal end of the PCCB gene, were found to 
inhibit alpha-beta heteromeric and/or the beta-beta homomeric interaction 
independently of the cultivation temperature, reflecting their primary effect on 
the assembly. Two mutations A497V and R165Q did not affect either heteromeric or 
homomeric assembly. The remaining mutations (R67S, S106R, G131D, R165W, E168K, 
and G198D), located in the amino-terminal region of the beta-polypeptide, 
resulted in normal interaction levels only when expressed at the lower 
temperature, suggesting that these changes could be considered as folding 
defects. From these results and the clinical manifestations associated with 
patients bearing the mutations described above, several genotype-phenotype 
correlations may be established. In general, the temperature-sensitive mutations 
are associated with a less severe, although variable phenotype. This could 
correlate with the recent hypothesis that the effect of folding mutations can be 
influenced by the capacity of the cellular protein quality control machinery, 
which provides clues to our understanding of the variability of the clinical 
symptoms observed among the patients bearing these mutations.