Cdc48 can distinguish between native and non-native proteins in the absence of cofactors

The ATPase Cdc48 is required for membrane fusion and protein degradation. Recently it has been suggested that Cdc48 in a complex with Ufd1 and Np14 acts as an ubiquitin-dependent chaperone. Here it is shown that recombinant Cdc48 alone can distinguish between the native and the non-native conformation of model substrates. First, Cdc48 prevents luciferase from aggregating following a heat shock. Second, it inhibits the aggregation of rhodanese upon dilution. Third, Cdc48 binds specifically to heat-denatured luciferase. These chaperone-like functions seem to be independent of ATPase activity. Furthermore, Cdc48 can act as a co-chaperone in the Hsc70-Hsp40 chaperone system. These results show that Cdc48 possesses chaperone-like activities and can functionally interact with Hsc70. Cdc48's ability to recognise denatured proteins can also be a source of unspecific binding in biochemical interaction experiments. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.