Propionyl-CoA carboxylase beta chain, mitochondrial

Propionyl-CoA carboxylase beta chain (PCCB) is a mitochondrial enzyme and one of two subunits of the biotin-dependent propionyl-CoA carboxylase (PCC) complex. It catalyzes the transfer of a carboxyl group from carboxylated biotin to propionyl-CoA, converting it to methylmalonyl-CoA. This enzyme participates in the catabolism of odd-chain fatty acids, branched-chain amino acids (isoleucine, threonine, methionine, valine), and related metabolites (UniProt: P05166).

PCCB is localized to the mitochondrion and functions as part of a key metabolic pathway. Mutations in PCCB cause propionic acidemia type II (PA-2), a life-threatening genetic disorder characterized by vomiting, lethargy, ketosis, and developmental delay (UniProt: P05166).

PCCB has been curated as disease-relevant in Alzheimer's Disease. In human post-mortem AD brain versus age-matched controls analyzed by TMT-labeled proteomics across four subcellular fractions, PCCB showed an ambiguous direction of change with a mean log2 fold-change of −0.14 (Chaparral AD proteomics). This modest, inconsistent shift across fractions suggests potential involvement in AD-related metabolic dysfunction, though the effect is subtle.