CHARACTERIZATION OF AN 88-KDA HEAT-SHOCK-PROTEIN OF NEUROSPORA-CRASSATHAT INTERACTS WITH HSP30

The small heat shock protein of Neurospora crassa, Hsp30, when employe d in affinity chromatography, bound two cellular proteins that were id entified as Hsp70 and Hsp88. Both Hsp70 and Hsp88 bound to Hsp30 in pr eference to other proteins, but binding of Hsp88 was more selective fo r Hsp30, and a direct interaction was observed, Transcripts for Hsp88, a newly characterized protein, are present at normal temperature, but they are strongly induced by heat shock. Its cDNA sequence predicts a protein with homology to mammalian Hsp110 family proteins, which are distantly related to Hsp70 Hsp88 and its homologues show greater simil arity to Hsp70 in its N-terminal ATPase domain than in the C-terminal peptide-binding domain, and its ATP-binding motifs are conserved. Neve rtheless, the N-terminal domain of Hsp88 land related proteins) is con sistently more hydrophobic and more basic than that of Hsp70 proteins. Within the C-terminal domain, the sequence corresponding to the DnaK alpha subdomain is conserved in the HspB8/Hsp110 family proteins, wher eas the DnaK beta subdomain sequence is not conserved. The interaction between Hsp70 and Hsp30 may reflect their cooperation as cochaperones for denatured proteins, whereas Hsp88 and Hsp30 may form a complex th at interacts with potential substrates.