A HEAT repeat is a protein tandem repeat structural motif composed of two alpha helices linked by a short loop. HEAT repeats can form alpha solenoids, a type of solenoid protein domain found in a number of cytoplasmic proteins. The name "HEAT" is an acronym for four proteins in which this repeat structure is found: <u>H</u>untingtin, elongation factor 3 (<u>E</u>F3), protein phosphatase 2A (PP2<u>A</u>), and the yeast kinase <u>T</u>OR1. HEAT repeats form extended superhelical structures which are often involved in intracellular transport; they are structurally related to armadillo repeats. The nuclear transport protein importin beta contains 19 HEAT repeats.
Representative examples of HEAT repeat proteins include importin ò (also known as karyopherin ò) family, regulatory subunits of condensin and cohesin, separase, PIKKs (phosphatidylinositol 3-kinase-related protein kinases) such as ATM () and ATR (), and the microtubule-binding protein XMAP215/Dis1/TOG and CLASP. Thus, cellular functions of HEAT repeat proteins are highly variable.
The structure of the following HEAT repeat proteins have been determined so far: