The N-terminal regions of β and γ subunits lower the solubility of adenosylcobalamin-dependent diol dehydratase

Adenosylcobalamin-dependent diol dehydratase is one of essential components of carboxysome-like polyhedral bodies. It exists as a heterohexamer (αβγ)₂, and its activity is recovered in a precipitant fraction of Klebsiella oxytoca and overexpressing Escherichia coli cells. Limited proteolysis of the enzyme with trypsin converted the enzyme into a highly soluble form without loss of enzyme activity. The N-terminal amino acid sequencing of the enzyme thus solubilized indicated that the N-terminal 20 and 16 amino acid residues had been removed from the β and γ subunits, respectively. Mutant enzymes with the same N-terminal truncations of either or both of the β and γ subunits were expressed on a high level in E. coli cells. All the mutant enzymes obtained were expressed in a soluble, active form. These results indicate that the N-terminal regions of the β and γ subunits lower the solubility of diol dehydratase. The mutant enzyme with the N-terminal truncations of both β and γ subunits was essentially indistinguishable in catalytic properties from recombinant wild-type enzyme or the enzyme purified from K. oxytoca in a soluble form.