HSP60: Molecular Weight
IHC staining of Listeria infected mice spleens 6 days after infection with L-monocytogenes, using Anti-Hsp60 (clone: LK2)
The HSP60/CPN60 family represents a group of well-conserved proteins with molecular weights ranging from 57 – 69 kDa. Functional genes encoding HSP60 proteins map to human chromosomes 1, 2, 5, 6, 7, 17, and 21. Hsp60 (also known as HspD1, Cpn60 or mitochondrial Hsp60) is a molecular chaperonin that assist protein folding in mitochondria 66. In humans, Hsp60 is encoded by a nuclear gene (HSPD1) clustered on chromosome 2q33.1 and translated in the cytosol 67. This gene is adjacent to a related family member, and the region between the two genes functions as a bidirectional promoter 67. Several pseudogenes have been associated with this gene 68. As the result of alternative splicing, two transcript variants encoding the same protein have been identified for the HSPD1 gene 67. The corresponding protein consists of 573 amino acid residues and harbors a mitochondrial localization sequence (MLS) of 26 amino acids at the N-terminus necessary for its import into mitochondria 69 as well as a series of G repeats at the C-terminus with unknown function 63. Iterations of these repeats can also be found in several eukaryotic Hsp70 C-terminal sequences. Based on GroEL crystal structure data as well as sequence alignments of several Hsp60 sequences from different species, HSP60s have been found to contain highly conserved regions that may be involved in mediating Hsp60-specific functions 2, 49. Intramitochondrial cleavage of the MLS generates the mature Hsp60 protein with 547 amino acids and a molecular mass of 61 kDa which is further processed by post-translational modifications. Like many other chaperones, Hsp60 is a phosphoprotein 70 whose expression and function can be further modulated by suomylation 71, acetylation 72, malonylation 73, N-glycosylation 74 or O-GlcNAcylation 75.