A biological cell uses a set of messengers, such as cyclic AMP, in order to
transmit the detection of changes in its environment (registered at the
cell surface) to intracellular compartments. One key participant is the
cyclic AMP-dependent protein kinase (PKA), which phosphorylates residues on
target proteins, causing changes in conformation and function.

Katayama et al. have developed a model system by taking a PKA substrate
peptide and grafting it to a temperature-responsive polymer chain. When
phosphorylated, the upper solubility temperature of the graft copolymer
increases from 33 deg-C to above 37 deg-C, which is nominal body temperature. A
third unit, when incorporated into the unphosphorylated copolymer, caused
it to form micellar particles, which disintegrated on treatment with PKA.
When these micelles were preloaded with a fluorescent dye and then
incubated with PKA, a gradual release of the fluorescent molecules was
observed. The authors envision that swapping the PKA-responsive peptide for
one recognized by aberrantly expressed kinases may yield targeted drug
delivery vehicles that would deliver their contents only to dysfunctional
cells. -- MSL

Macromolecules, in press