Summary: the authors found that the tag binds to large
intracellular structure(s), making it invisible
to NMR and thus simplifying the in-cell NMR
spectrum of the target protein.
This method opens the door to determin-
ing protein structures inside human cells in the
near future, but has already been used by Ino-
mata et al. to study in-cell protein dynamics.
For example, macromolecular crowding inside
the cell should stabilize protein structures.
Inomata et al. show that, for at least one pro-
tein, ubiquitin, introduced into a human cell
at physiological concentrations, the opposite is
true. Ubiquitin becomes more dynamic in its
reactivity and less structured, presumably due
to nonspecific, low-affinity interactions with
its binding partners. This unexpected result
highlights the importance of studying proteins
inside living cells.
In-cell NMR is limited by the concentration