One might think of mitochondria as devices for transporting electrons to their lowest energy state. Little bags of finely-tuned respiratory chain subunits which combine electrons extracted from food with oxygen, and ultimately excrete them as water. Others might justifiably fancy mitochondria tiny bundles of geometry. Their folded inner membranes pegged with various proteins complexes like the rolls of candy button paper we might have ate as kids. Actually mitochondria are both enzyme bags and geometrical objects: the latest research tells us that it is proteins which create the complex inner membrane geometry specific to each kind of mitochondria, and in turn, it is their precise geometry which permits the respiratory proteins to create useful work in the first place.
A couple of papers from
the past week have reported on the roles of some of the more important
proteins in shaping membranes. Of note, one published by Polish and
German researchers in The Journal of Biological Chemistry found a
critical new protein that controls formation of the so-called MICOS
system (mitochondrial contact site and cristae organizing system). This
protein, Cox17, was already known for its role as a chaperone in the
assembly of respiratory complex IV on the inner membrane of mitochondria.
Known as cytochrome c oxidase (COX), this is the terminal respiratory
complex in the whole chain—the one that hands off the electrons to
oxygen. Among other amenities, Cox17 has a series of critical cysteines
which appear to involved in recruiting copper to the business end of the
mitochondrially encoded COX subunits.