Studies of the equilibrium between native and denatured forms of wild-type levansucrase showed that the denatured form was predominant at 37 degrees C and pH 7 in the absence of free metal. The shift to the native form was promoted by metal ions such as Fe3+ or Ca2+. This metal-dependent refolding process was not observed in levansucrase variants bearing the amino acid substitution Gly-366----Asp or Gly-366----Val. These variants were only slightly secreted by Bacillus subtilis although their signal sequences were normally cleaved and their exocellular forms stable. In contrast, the Gly-366----Ser variant was secreted at near-normal levels and shared a part of the in vitro refolding properties of the wild-type protein. These differential properties might be related to the ability of the altered region to form a beta-turn structure. We discuss the possible role of metal ions in the coupling of protein folding and secretion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.