12.2018 | THE SCIENTIST 43TOBIAS GIESSEN
xanthus and T. maritima nanocompartments. The third group
contains hemerythrins, enzymes that can protect cells from
stress caused by reactive oxygen and nitrogen species. All three
types are likely to play a role in the cell’s response to stress,
notes Giessen.
This year, he identified a new class with enzymes that pro-
duce aldehyde intermediates. These nanocompartments might
serve to sequester the toxic compounds, as has been found of
related microcompartments. But for all nanocompartments,
Giessen admits, “we don’t really know too much about their
real biological functions yet.”
As scientists continue to probe the functions of these newly
discovered structures, Hoiczyk is still struck by how much they
look like viruses. “The similarity is kind of mind-boggling,” he
says, noting that the encapsulin shell protein contains a fold that
is exceedingly similar to one found in the HK97 bacteriophage
capsid. It’s likely that the resemblance is not due to chance.
Hoiczyk and others suspect the nanocompartments share an
evolutionary history with bacteriophages, though they don’t
know which came first.
The origin of the larger microcompartments is less obvious,
though their component parts share some features with cellular pro-
teins.^15 For both types of structures, there’s still plenty to learn—not
only about their basic biology, but also how to engineer them to per-
form industrially relevant functions.
And who’s to say that nano- and microcompartments are
the only types of protein-encapsulated bacterial organelles?
“It’s somewhat interesting to muse about some that haven’t
been discovered yet,” Yeates says. “It would be cool if there
were others.” gNANOCOMPARTMENTS UP CLOSE: Micrographs of encapsulin shells
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