Human dihydrolipoamide dehydrogenase (hLADH, hE3) deficiency (OMIM# 246900) is an
often prematurely lethal genetic disease usually caused by inactive or partially inactive
hE3 variants. Here we report the crystal structure of wild-type hE3 at an unprecedented
high resolution of 1.75 Å and the structures of six disease-causing hE3 variants at
resolutions ranging from 1.44 to 2.34 Å. P453L proved to be the most deleterious substitution
in structure as aberrations extensively compromised the active site. The most prevalent
G194C-hE3 variant primarily exhibited structural alterations close to the substitution
site, whereas the nearby cofactor-binding residues were left unperturbed. The G426E
substitution mainly interfered with the local charge distribution introducing dynamics
to the substitution site in the dimer interface; G194C and G426E both led to minor
structural changes. The R460G, R447G, and I445M substitutions all perturbed a solvent
accessible channel, the so-called H+/H2O channel, leading to the active site. Molecular
pathomechanisms of enhanced reactive oxygen species (ROS) generation and impaired
binding to multienzyme complexes were also addressed according to the structural data
for the relevant mutations. In summary, we present here for the first time a comprehensive
study that links three-dimensional structures of disease-causing hE3 variants to residual
hLADH activities, altered capacities for ROS generation, compromised affinities for
multienzyme complexes, and eventually clinical symptoms. Our results may serve as
useful starting points for future therapeutic intervention approaches.
