Bacillus subtilis levansucrase: amino acid substitutions at one site affect secretion efficiency and refolding kinetics mediated by metals.
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.
Petit-Glatron
M F
MF
Laboratoire Génétique et Membranes, Institut Jacques Monod, CNRS-Université Paris VII, France.
Monteil
I
I
Benyahia
F
F
Chambert
R
R
D000596:Amino Acids / Q000737:chemistry; D001412:Bacillus subtilis / Q000201:enzymology*; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006602:Hexosyltransferases / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D011489:Protein Denaturation; D013696:Temperature
D000596:Amino Acids; D007501:Iron; D006602:Hexosyltransferases; C021513:levansucrase; D002118:Calcium