Nanoscale conformational dynamics of human propionyl-CoA carboxylase

Propionyl-CoA carboxylase (PCC) is a biotin-dependent mitochondrial enzyme responsible for propionyl-CoA catabolism. Deficiencies in human PCC (hPCC) cause propionic acidemia, a severe metabolic disorder driven by toxic metabolite accumulation. Despite its therapeutic relevance, the structural basis of hPCC's catalytic function remains unresolved. Here, we present high-resolution cryo-EM structures of hPCC in four distinct states, unliganded, ADP-, AMPPNP-, and ATP-bound/substrate-bound, capturing the full trajectory of the biotin carboxyl carrier protein (BCCP) domain as it translocates between active sites. Our results reinforce the crucial role of nucleotide-gated B-lid subdomain in synchronizing catalysis through coupling with BCCP movement. Structural and biochemical analysis of 10 disease-associated variants reveals how mutations disrupt key domain interfaces and dynamic motions required for activity. These new insights define the mechanistic principles governing hPCC functions, establish a structural framework for understanding PCC-related disorders, and lay the groundwork for future efforts to engineer functional replacements or modulators for metabolic therapy.