Domain organization of flagellar hook protein from Salmonella typhimurium

Hook forms a universal joint, which mediates the torque of the flagellar mo tor to the outer helical filaments, Domain organization of book protein fro m Salmonella typhimurium was investigated by exploring thermal denaturation properties of its proteolytic fragments, The most stable part of hook prot ein involves residues 148 to 355 and consists of two domains, as revealed b y deconvolution analysis of the calorimetric melting profiles, Residues 72- 147 and 356-370 form another domain, while the terminal regions of the mole cule, residues 1-71 and 371-403, avoid a compact tertiary structure in the monomeric state, These folding domains were assigned to the morphological d omains-of hoot subunits known from EM image reconstructions, revealing the overall folding of hook protein in its filamentous state, (C) 1999 Federati on of European Biochemical Societies.