Hsp104 is a hexameric AAA+
protein that utilizes energy from
ATP hydrolysis to dissolve disordered
protein aggregates as well as
amyloid fibers. Interestingly, Hsp104 orthologues are found in all kingdoms of life except animals. Thus, Hsp104 could represent an interesting
drug target. Specific inhibition of Hsp104 activity might antagonize non-metazoan parasites that depend on a potent heat shock response, while producing little or no side effects to the host. However, no small molecule inhibitors of Hsp104 are known except
guanidinium chloride. Here, we screen over 16,000 small molecules and identify 16 novel inhibitors of Hsp104
ATPase activity. Excluding compounds that inhibited Hsp104 activity by non-specific colloidal effects, we defined
Suramin as an inhibitor of Hsp104
ATPase activity.
Suramin is a polysulphonated naphthylurea and is used as an antiprotozoal
drug for
African Trypanosomiasis.
Suramin also interfered with Hsp104 disaggregase, unfoldase, and translocase activities, and the inhibitory effect of
Suramin was not rescued by Hsp70 and Hsp40.
Suramin does not disrupt Hsp104 hexamers and does not effectively inhibit ClpB, the E. coli homolog of Hsp104, establishing yet another key difference between Hsp104 and ClpB behavior. Intriguingly, a potentiated Hsp104 variant, Hsp104A503V, is more sensitive to
Suramin than wild-type Hsp104. By contrast, Hsp104 variants bearing inactivating sensor-1 mutations in
nucleotide-binding domain (NBD) 1 or 2 are more resistant to
Suramin. Thus,
Suramin depends upon
ATPase events at both NBDs to exert its maximal effect.
Suramin could develop into an important mechanistic probe to study Hsp104 structure and function.