V. Guenebaut et al., CONSISTENT STRUCTURE BETWEEN BACTERIAL AND MITOCHONDRIAL NADH-UBIQUINONE OXIDOREDUCTASE (COMPLEX-I), Journal of Molecular Biology, 276(1), 1998, pp. 105-112
Respiratory chains of bacteria and mitochondria contain closely relate
d forms of the proton-pumping NADH:ubiquinone oxidoreductase (complex
I). In bacteria the complex has a molecular mass of approximately 530
kDa and consists of 14 different subunits. The homologues of these 14
subunits together with some 27 additional subunits make up the mitocho
ndrial complex, adding up to a molecular mass of approximately 1 MDa.
We calculated three-dimensional models at medium resolution of isolate
d and negatively stained complex I particles from Eschericha coli and
Neurospora crassa by electron microscopy using the random conical tilt
reconstruction technique. Both the bacterial and the mitochondrial co
mplexes are L-shaped molecules with an intrinsic membrane arm extendin
g into the lipid bilayer and a peripheral arm protruding from the memb
rane. It is discussed whether the consistent length of the arms of bot
h complexes has an implication for their function. The additional prot
ein mass of the mitochondrial complex is distributed along both arms,
but especially around the junction between the two arms and around the
membrane arm. It appears that the structural framework of procaryotic
complex I is stabilized in eucaryotes by this additional mass. A disc
rete location of additional protein in the peripheral arm of the mitoc
hondrial complex is interpreted as being the possible position of two
subunits with a specialized role in the biosynthesis of a yet unknown
cofactor of complex I. (C) 1998 Academic Press Limited.