The BAG proteins: a ubiquitous family of chaperone regulators

The BAG (Bcl-2 associated athanogene) family is a multifunctional group of proteins that perform diverse functions ranging from apoptosis to tumorigenesis. An evolutionarily conserved group, these proteins are distinguished by a common conserved region known as the BAG domain. BAG genes have been found in yeasts, plants, and animals, and are believed to function as adapter proteins forming complexes with signaling molecules and molecular chaperones. In humans, a role for BAG proteins has been suggested in carcinogenesis, HIV infection, and Parkinson's disease. These proteins are therefore potential therapeutic targets, and their expression in cells may serve as a predictive tool for such diseases. In plants, the Arabidopsis thaliana genome contains seven homologs of the BAG family, including four with domain organization similar to animal BAGs. Three members contain a calmodulin-binding domain possibly reflecting differences between plant and animal programmed cell death. This review summarizes current understanding of BAG proteins in both animals and plants.