Alpha crystallin domain (ACD) found in mammalian small heat shock protein (sHsp) HspB2/heat shock 27kDa protein 2 and similar proteins. sHsps are molecular chaperones that suppress protein aggregation and protect against cell stress, and are generally active as large oligomers consisting of multiple subunits. HspB2 is preferentially and constitutively expressed in skeletal muscle and heart. HspB2 shows homooligomeric activity and forms aggregates in muscle cytosol. Although its expression is not induced by heat shock, it redistributes to the insoluble fraction in response to heat shock. In the mouse heart, HspB2 plays a role in maintaining energetic balance, by protecting cardiac energetics during ischemia/reperfusion, and allowing for increased work during acute inotropic challenge. hHspB2 [previously also known as myotonic dystrophy protein kinase (DMPK) binding protein (MKBP)] is selectively up-regulated in skeletal muscles from myotonic dystrophy patients. The ACD of hHspB2 binds the DMPK kinase domain. In vitro, hHspB2 enhances the kinase activity of DMPK and confers thermoresistance. The hHspB2 gene lies less than 1kb from the 5 prime end of the related alphaB (HspB4)-crystallin gene, with the opposite transcription direction. These two genes may share regulatory elements for their expression.
Jiyao W et al.(2023). "The conserved domain database in 2023.",