Compared effects of missense mutations in Very-Long-Chain Acyl-CoA Dehydrogenase deficiency: Combined analysis by structural, functional and pharmacological approaches

Abstract

Very-Long-Chain Acyl-CoA Dehydrogenase deficiency (VLCADD) is an autosomal recessive disorder considered as one of the more common β-oxidation defects, possibly associated with neonatal cardiomyopathy, infantile hepatic coma, or adult-onset myopathy. Numerous gene missense mutations have been described in these VLCADD phenotypes, but only few of them have been structurally and functionally analyzed, and the molecular basis of disease variability is still poorly understood. To address this question, we first analyzed fourteen disease-causing amino acid changes using the recently described crystal structure of VLCAD. The predicted effects varied from the replacement of amino acid residues lining the substrate binding cavity, involved in holoenzyme-FAD interactions or in enzyme dimerisation, predicted to have severe functional consequences, up to amino acid substitutions outside key enzyme domains or lying on near enzyme surface, with predicted milder consequences. These data were combined with functional analysis of residual fatty acid oxidation (FAO) and VLCAD protein levels in patient cells harboring these mutations, before and after pharmacological stimulation by bezafibrate. Mutations identified as detrimental to the protein structure in the 3-D model were generally associated to profound FAO and VLCAD protein deficiencies in the patient cells, however, some mutations affecting FAD binding or monomer-monomer interactions allowed a partial response to bezafibrate. On the other hand, bezafibrate restored near-normal FAO rates in some mutations predicted to have milder consequences on enzyme structure. Overall, combination of structural, biochemical, and pharmacological analysis allowed to assess the relative severity of individual mutations, with possible applications for disease management and therapeutic approach.

Novel mutations in the gene encoding very long‐chain acyl‐CoA dehydrogenase identified in patients with partial carnitine palmitoyltransferase ii deficiency

“…The p.T409M mutation has not been reported in the literature but is listed in the NCBI dbSNP database as a pathogenic mutation. The p.G439D mutation has been identified previously26 and is described as a mild or possibly severe mutation 10. Although this residue side‐chain appears to be exposed to solvent as depicted in Figure 2, consideration of the dimer structure of VLCAD shows that alteration to an aspartate residue could affect monomer‐monomer interactions as well as FAD binding 10.…”

“…The p.G439D mutation has been identified previously26 and is described as a mild or possibly severe mutation 10. Although this residue side‐chain appears to be exposed to solvent as depicted in Figure 2, consideration of the dimer structure of VLCAD shows that alteration to an aspartate residue could affect monomer‐monomer interactions as well as FAD binding 10. However, the p.G439D mutation has only been characterized in fibroblasts for total fatty acid flux in the context of a patient also carrying another uncharacterized mutation, p.A304T 26.…”

“…However, the majority of the approximately 100 identified disease‐causing mutations each in CPT2 and ACADVL are amino acid substitutions which have a range of clinical effects. The phenotypic effects of some of the more common amino acid substitutions have been clearly established, but the effects of most of the currently known mutations have not been determined 8, 10…”

Functional studies of 18 heterologously expressed medium‐chain acyl‐CoA dehydrogenase (MCAD) variants

“…Due to the fact that novel mutations often appear in compound heterozygosity together with severe mutations, such as the prevalent K304E, functional analysis of single mutations is often impaired. In summary, this study provides information with respect to biochemical properties and three-dimensional structure of 12 successfully expressed mutant MCAD variants, which adds information and might help in developing individual management guidelines for individuals identified with MCAD deficiency on NBS, as discussed for other fatty acid oxidation disorders, such as very long-chain acyl-CoA dehydrogenase deficiency and multiple acyl-CoA dehydrogenase deficiency (Gobin-Limballe et al 2010;Cornelius et al 2012).…”

Disorders of Lipid Metabolism

“…25,53,59,60 There is some genotype-phenotype correlation and mutations that result in some residual enzyme activity are usually found in patients with the milder phenotypes. 25,53,59,60 There is some genotype-phenotype correlation and mutations that result in some residual enzyme activity are usually found in patients with the milder phenotypes.…”