The N-terminus of the human dihydroorotate dehydrogenase (HsDHODH) has been described as
important for the enzyme attachment in the inner mitochondrial membrane and possibly to regulate enzymatic
activity. In this study, we synthesized the peptide acetyl-GDERFYAEHLMPTLQGLLDPESAHRL AVRFTSLGamide,
comprising the residues 33-66 of HsDHODH N-terminal conserved microdomain. Langmuir monolayers and circular
dichroism (CD) were employed to investigate the interactions between the peptide and membrane model, as micelles
and monolayers of the lipids phosphatidylcholine (PC), 3-phosphatidylethanolamine (PE) and cardiolipin (CL). These lipids
represent the major constituents of inner mitochondrial membranes. According to CD data, the peptide adopted a random
structure in water, whereas it acquired α-helical structures in the presence of micelles. The π–A isotherms and polarization-
modulated infrared reflection-absorption spectroscopy on monolayers showed that the peptide interacted with
all lipids, but in different ways. In DPPC monolayers, the peptide penetrated into the hydrophobic region. The strongest
initial interaction occurred with DPPE, but the peptide was expelled from this monolayer at high surface pressures. In CL,
the peptide could induce a partial dissolution of the monolayer, leading to shorter areas at the monolayer collapse. These
results corroborate the literature, where the HsDHODH microdomain is anchored into the inner mitochondrial membrane.
Moreover, the existence of distinct conformations and interactions with the different membrane lipids indicates that the
access to the enzyme active site may be controlled not only by conformational changes occurring at the microdomain of
the protein, but also by some lipid-protein synergetic mechanism, where the HsDHODH peptide would be able to recognize
lipid domains in the membrane.
Keywords: Circular dichroism, human dihydroorotate dehydrogenase, Langmuir monolayers, peptide, phospholipids, polarization-
modulated infrared reflection-absorption spectroscopy, solid-phase peptide synthesis.
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