Research

Development of Chemical Chaperone for Medium Chain Acyl-CoA Dehydrogenase Deficiency

Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is an inborn error of fatty acid metabolism, rivaling phenylalanine hydroxylase deficiency (PKU) as the most common biochemical genetic disorder.

MCADD patients are asymptomatic at birth but are at risk for episodes of acute, life threatening metabolic decompensation. These usually first occur between 3 and 24 months of age but can occur at any age in association with physiologic stress such as fasting or infection. The mortality rate during an acute crisis in previously undiagnosed patients can be as high as 20 percent.

With the introduction of expanded newborn screening via tandem mass spectrometry, MCADD can now be identified pre-symptomatically, nearly eliminating mortality due to this disease. However, treatment requires lifelong dietary monitoring, and significant morbidity still occurs due to hospitalizations for intravenous glucose therapy in the face of reduced oral intake. A single mutation in the MCAD gene (a G985A point mutation) has been identified in 90 percent of the alleles in the MCAD gene in deficient patients. This mutation substitutes a glutamate for a lysine at position 304 of the mature enzyme (K304E). According to the crystal structures of recombinant human MCAD, the K304 side chain extends at the edge of a unique cavity in the inner core of the tetramer, which is greater than 14 angstroms in diameter comprised by the four monomers, where its side chain amino group hydrogen bonds with the side chain amide oxygen of Q342. The K304E mutation introduces instead four abnormal negative charges into the core, destabilizing the quaternary structure of the enzyme. As a result, the mutant protein is rapidly degraded.

In vitro studies have shown that the mutant protein is catalytically active when it can be stabilized. Importantly, published in vivo and in vitro data suggest that restoration of only a few percent of normal MCAD activity will restore near normal metabolic balance in patients. The long-term objective of this research program is to develop molecular strategies for treatment of MCAD deficiency and that of other structurally similar acyl-CoA dehydrogenases (ACDs). The specific objective is to establish the “drugability” of the MCAD K304E mutant by identifying lead compounds that can stabilize the mutant protein using in vitro and in silico approaches. Using the in vitro chemical screening approach, a library of pharmacologically active compounds (LOPAC) will be screened for increasing the detection of MCAD enzyme activity and antigen level in cells homozygous for the K304E mutation. A high-content image based fluorescence immunoassay is at the late stages of development for this screening and will also be used for high-throughput screening of larger libraries. Using the in silico chemical screening approach, a library of small fragments will be used for potential binding at selected cavities using the mutant 3D structure.

Additions of groups at expansion sites may improve binding potential of the hypothetical ligand and will be pursued depending on calculated parameters. Already several compounds have been designed and this research is pursuing synthesis of these compounds.

Principal Investigator
Al-Walid A. Mohsen, PhD

Last Update
August 14, 2010
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Last Update
August 14, 2010
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