Final answer:
HSP-90 binds HSF1 under non-stressful conditions to inhibit the expression of heat shock proteins. During heat stress, HSP-90 is released, activating HSF1 to induce the transcription of heat shock proteins that help refold denatured proteins and restore cell functions.
Step-by-step explanation:
HSP-90 (Heat Shock Protein 90) is known for its role in responding to stress within cells, especially during conditions of elevated temperatures, a phenomenon called heat shock. HSP-90 and other heat shock proteins are crucial in protecting cells from metabolic damage under these stressful conditions by assisting in the correct folding of proteins. HSP-90 is capable of binding to HSF1 (Heat Shock Factor 1), which is a transcription factor that regulates heat shock protein genes.
Under normal conditions, HSP-90 binds to HSF1, inhibiting its activity and thus preventing the unnecessary expression of heat shock proteins. However, during heat stress, when protein misfolding becomes prevalent, the cell releases HSP-90 from HSF1, allowing HSF1 to initiate the transcription of heat shock proteins. These proteins then function as molecular chaperones to refold denatured proteins and help recover protein homeostasis.