Explore the vast range of titles available.

Short-chain acyl-CoA dehydrogenase (SCAD) is a critical enzyme in mitochondrial fatty acid β-oxidation, catalyzing the initial dehydrogenation of short-chain acyl-CoAs. Mutations in the ACADS gene cause SCAD deficiency (SCADD), a disorder with remarkably heterogeneous clinical presentation. However, the molecular mechanisms underlying substrate specificity and the pathogenicity of most ACADS variants remain poorly understood. Here, we present high-resolution cryo-EM structures of human SCAD in complex with its physiological substrate butyryl-CoA (C4) and the longer substrate hexanoyl-CoA (C6). The butyryl-CoA-bound structure at 2.1 Å resolution details a pre-catalytic geometry ideal for hydride transfer, with Glu392 positioned as the catalytic base. We systematically characterized nineteen disease-associated mutations, which we classify into three functional categories: those disrupting FAD binding, those impairing substrate binding, and those compromising protein folding and stability. In addition, using the W177R mutant as a representative model, we demonstrate that folding-defective mutations provoke protein aggregation, leading to proteotoxicity, oxidative stress, and apoptosis, revealing a pathogenic mechanism beyond mere catalytic loss. In brief, our integrated findings elucidate the structural determinants of substrate specificity and catalytic mechanism in SCAD, and provide mechanistic insights into the functional impairments caused by mutations linked to SCADD.

Deficiency of short-chain enoyl-CoA hydratase (ECHS1), a crucial enzyme in fatty acid metabolism through the mitochondrial β-oxidation pathway, has been strongly linked to various diseases, especially cardiomyopathy. However, the structural and biochemical mechanisms through which ECHS1 recognizes acyl-CoAs remain poorly understood. Herein, cryo-EM analysis reveals the apo structure of ECHS1 and structures of the ECHS1-crotonyl-CoA, ECHS1-acetoacetyl-CoA, ECHS1-hexanoyl-CoA, and ECHS1-octanoyl-CoA complexes at high resolutions. The mechanism through which ECHS1 recognizes its substrates varies with the fatty acid chain lengths of acyl-CoAs. Furthermore, crucial point mutations in ECHS1 have a great impact on substrate recognition, resulting in significant changes in binding affinity and enzyme activity, as do disease-related point mutations in ECHS1. The functional mechanism of ECHS1 is systematically elucidated from structural and biochemical perspectives. These findings provide a theoretical basis for subsequent work focused on determining the role of ECHS1 deficiency (ECHS1D) in the occurrence of diseases such as cardiomyopathy. The study of ECHS1 functional mechanism provides a theoretical basis for subsequent work focused on determining the role of ECHS1 deficiency (ECHS1D) in the occurrence of diseases such as cardiomyopathy.

Isovaleryl-CoA (coenzyme A) dehydrogenase (IVD) plays a pivotal role in the catabolism of leucine, converting isovaleryl-CoA to 3-methylcrotonyl-CoA. Dysfunction of IVD is linked to isovaleric acidemia (IVA), a rare metabolic disorder characterized by the accumulation of toxic metabolites. In this study, we present the cryo-electron microscopy structures of human IVD, resolved both in its apo form and in complex with its substrates, isovaleryl-CoA and butyryl-CoA. Our findings reveal a tetrameric architecture with distinct substrate-binding pockets that facilitate the enzyme's preference for short branched-chain acyl-CoAs. Key residues involved in FAD binding and substrate interaction were identified, elucidating the catalytic mechanism of IVD. Additionally, we investigated the impact of various disease-associated hotspot mutations derived from different regions, demonstrating their effects on enzyme stability and activity. Notably, mutations such as A314V, S281G/F382V, and E411K resulted in substantial loss of function, while others exhibited milder effects, which is consistent with our structural analyses. These insights enhance our understanding of IVD's enzymatic properties and provide a foundation for developing targeted therapies for IVA.