Cells express an increased amount of several highly conserved proteins referred to as heat shock or heat stress proteins (Hsps). They are primarily found in the cytoplasm, nucleus, and mitochondria. Mammalian cells Hsps are classified into several families of sequence-related proteins, which are differentiated by their molecular sizes. Major families are as follows: the Hsp25/Hsp27/Hsp28 family (the small stress proteins), the Hsp40 family, the Hsp60 family, the Hsp70 family, the Hsp90 family, and the Hsp110/SSE family. HSP40, also known as DNAJB1, HSPF1, or HDJ1, is a 339-amino acid, stress inducible heat shock protein, that is homologous to the bacterial heat shock protein DnaJ, and to the yeast DnaJ-related proteins such as SCJ1, Sec63/Np11, YDJ1, and SIS1.
In heat-shocked cells, Hsp40 translocates from the cytoplasm to the nucleus and nucleoli, colocalizing with Hsp70. Hsp40 and Hsp70 have been implicated in reduction of protein aggregates produced in neurodegenerative diseases, such a Huntington′s and Parkinson′s diseases. In brain tissues from Parkinson disease patients, it has been shown that Lewy bodies (LBs) and Lewy neurites (LNs) are immunopositive for Hsp70 and Hsp40 chaperones, suggesting that altered chaperone activity may be involved in progression of Parkinson disease.
