Mitochondrial atlas finds 33 protein families that pathogens share and humans lack

Set against the 3,199 families in the pooled collection, 33 is about 1% ^[18]. Mootha, who led the project, said such proteins can be "ideal drug targets" for precise therapies that would act on parasite proteins but not human ones ^[12].

Most of what is known about mitochondria comes from human and yeast studies, according to Mootha, a mitochondrial biologist at the Howard Hughes Medical Institute in Boston ^[3]. The new maps add five single-celled parasites and one plant ^[1]. About 43% of the 3,199 families are not recorded in Pfam, a large protein database ^[10]. That works out to roughly 1,400 families ^[20].

Giardia lamblia is the example Nature walks through. The parasite infects about 280 million people worldwide each year and causes diarrhoea ^[4]. Its mitochondrion-like organelles are hard to study because it lives in the gut of other organisms, without oxygen, said Pavel Doležal, a cell biologist at Charles University in Prague ^[5]. Of the 59 proteins the team found, 34 have no known function, about 58% ^[19]. Doležal called that surprising because "it means that there is some new metabolism that we don't know about. And it was overlooked" ^[8].

The papers do not test whether any of the 33 families is essential to a parasite. We think essentiality is the test of whether these are drug targets, since a protein missing from humans is only useful if the parasite cannot do without it.

On origins, the shared ground is narrow. Researchers agree that mitochondria emerged two billion years ago, when an archaeal cell engulfed a bacterium ^[13]. It remains unclear whether the mitochondrion arose early or late in eukaryotic evolution ^[14]. Mootha's team mapped the lineage of the mitoproteomes onto a phylogenetic tree to address that ^[15]. Nature says the work has stirred the long-running debate ^[17]. The text of Nature's report cuts off before it says what the tree analysis found about timing.