• Journal of Life Science
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• v.6 no.4
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• pp.304-312
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• 1996

In the present report, a p[ossibility of the interaction fo Ser-33 and Asp-112 residues in folding of tryptophan synthase $\alpha$ subunit was explored by examining the effect of single or double substitution of these residues on folding of $\alpha$ subunit in E. coli. $\alpha$ subunit of which Ser-33 was substituted with Leu (SL33) was accumulated as insoluble aggregate form, when overproduced in E. coli, whereas $\alpha$ subunit of which Asp-112 was replaced by Asn (DN112) or Gly (DG112) was accumulated as soluble form to the similar extent as wild type $\alpha$ subunit was. When these alterations were combined into one protein, the synergistic effect of residues 33 and 112 on the amount of aggregate form was shown. The amount of doubly altered SL33/DG112 $\alpha$ subunit as aggregate form was increased 5-13 fold that of SL33 $\alpha$ subunit, and the amount of SL33/DG112 $\alpha$ subunit as aggregate form was decreased 3-4 fold that of SL33 $\alpha$ subunit. Aggregates are derived from the specific association of partially folded or unassembled subunits in the folding process. Therefore, this result suggests that residues 33 and 112 of $\alpha$ subunit may unteract during the folding of this enzyme in E. coli.