heat-shock protein
/ abbreviated Hsp /
Leave a chocolate bar in a hot car and it melts and loses its shape; heat does the same kind of thing to proteins, jiggling them so hard that their carefully folded shapes start to come apart. Cells fight back with an emergency crew of proteins that rush in to rescue and protect the others. These are the heat-shock proteins, named because they were first noticed when scientists briefly heated fruit-fly cells and saw a sudden burst of new protein production.
Most heat-shock proteins are molecular chaperones — they grab onto proteins whose shapes are starting to unravel, hold them so they cannot clump together, and help them refold once the danger passes. They are grouped and named by their rough size in kilodaltons: Hsp70, Hsp90, Hsp60, and the small Hsps, each with its own specialty. When a cell senses trouble — heat, toxins, low oxygen, a flood of misfolded proteins — a master switch (a transcription factor called heat-shock factor) turns up production of these proteins sharply. So the name is a bit narrow: heat was just the first stress noticed, but the same proteins respond to many kinds of stress, and many of them are also busy doing routine folding work even on a perfectly comfortable day.
Heat-shock proteins matter far beyond surviving a hot day. Hsp90, for instance, keeps many signaling proteins poised and ready, which makes it a target for cancer drugs because tumors lean on it heavily. Because they buffer cells against the damage of misfolding, heat-shock proteins are studied in aging and in neurodegenerative diseases, where boosting them is being explored as a way to clear toxic aggregates. The common oversimplification to avoid: they are not only switched on by literal heat, and they are not a single protein but a whole family of distinct molecules.
When a feverish patient's cells warm up, levels of Hsp70 climb within minutes. The extra Hsp70 grabs proteins whose shapes are starting to wobble and holds them safely until the fever breaks, sparing the cell from a wave of aggregation.
A fever triggers a defensive surge of Hsp70.
Heat-shock proteins are defined by the stress response, not by a single function. Many are housekeeping chaperones at all times; only their surge under stress earned them the name.