The Hs1U ATPase acts as a molecular chaperone in prevention of aggregationof Su1A, an inhibitor of cell division in Escherichia coli

HslVU is an ATP-dependent protease consisting of two multimeric components: the HslU ATPase and the HslV peptidase, SulA, which is an inhibitor of cel l division and has high tendency of aggregation, is degraded by HslVU prote ase, Here we show that HslU plays a role not only as a regulatory component for the HslV-mediated proteolysis but also as a molecular chaperone. Purif ied HslU prevented aggregation of SulA in a concentration-dependent fashion . This chaperone activity required oligomerization of HslU subunits, which could be achieved by ATP-binding or in the presence of high HslU protein co ncentrations. hsl mutation reduced the SulA-mediated inhibition of cell gro wth and this effect could be reversed upon overproduction of HslU, suggesti ng that HslU promotes the ability of SulA to block cell growth through its chaperone function. Thus, HslU appears to have two antagonistic functions: one as a chaperone for promotion of the ability of SulA in cell growth inhi bition by preventing SulA aggregation and the other as the regulatory compo nent for elimination of SulA by supporting the HslV-mediated degradation. ( C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.