Identification and characterization of Harc, a novel Hsp90-associating relative of Cdc37.
Although little is known about the precise mechanisms by which the molecular chaperone Hsp90 recognizes its client proteins, Cdc37 has been shown to play a critical role in the targeting of Hsp90 to client protein kinases. Described here is the identification and characterization of a novel 35-kDa human protein that is 31% identical to Cdc37. We have named this novel protein Harc (Hsp90-associating relative of Cdc37). Northern blot analysis revealed the presence of Harc mRNA in several human tissues, including liver, skeletal muscle, and kidney. Biochemical fractionation and immunofluorescent localization of epitope-tagged Harc (i.e. FLAG-Harc) indicated that it is present in the cytoplasm of cells. FLAG-Harc binds Hsp90 but unlike Cdc37 does not bind Src family kinases or Raf-1. Mapping experiments indicate that the central 120 amino acids of both Harc and Cdc37 constitute a Hsp90-binding domain not described previously. FLAG-Harc is basally serine-phosphorylated and hyperphosphorylated when co-expressed with an activated mutant of the Src family kinase Hck. Notably, FLAG-Harc forms complexes with Hsp90, Hsp70, p60Hop, immunophilins, and an unidentified p22 protein but not with the Hsp90 co-chaperone p23. Thus Harc likely represents a novel participant in Hsp90-mediated protein folding, potentially targeting Hsp90 to Hsp70-client protein heterocomplexes.
Scholz
G M
GM
Ludwig Institute for Cancer Research, Post Office Box 2008, Royal Melbourne Hospital, Victoria 3050, Australia. Glen.Scholz@ludwig.edu.au
Cartledge
K
K
Hall
N E
NE
D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D002478:Cells, Cultured; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009842:Oligopeptides; D010455:Peptides / Q000737:chemistry; D010750:Phosphoproteins / Q000737:chemistry; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism
D002352:Carrier Proteins; C103269:Cdc37 protein, rat; D018797:Cell Cycle Proteins; D018841:HSP90 Heat-Shock Proteins; D009842:Oligopeptides; D010455:Peptides; D010750:Phosphoproteins; C085706:FLAG peptide; D019908:Proto-Oncogene Proteins c-raf