Miller syndrome is a rare Mendelian disorder caused by mutations in the gene encoding human
dihydroorotate dehydrogenase (
DHODH). Human
DHODH, a Class II
DHODH, is an integral
protein of the inner mitochondrial membrane (IMM) catalyzing the fourth step of the de novo
pyrimidine biosynthesis pathway. Here we present a summary of the state of knowledge regarding
Miller syndrome in the absence of any current review on the topic. We then describe the production and characterization of three distinct
DHODH missense mutations (G19E, E52G, R135C) associated with
Miller syndrome by means of
enzyme kinetics and biophysical techniques. These human
DHODH mutants were produced both in E. coli and in insect cells using the baculovirus expression vector system. We can show that the effects of these mutations differ from each other and the wild-type
enzyme with respect to decreased enzymatic activity, decreased protein stability and probably disturbance of the correct import into the IMM. In addition, our results show that the N-terminus of human
DHODH is not only a structural
element necessary for correct mitochondrial import and location of
DHODH on the outer side of the IMM, but also influences thermal stability, enzymatic activity and affects the kinetic parameters.Supplemental data for this article is available online at https://doi.org/10.1080/15257770.2021.2023749 .