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KMID : 0613820170270121410
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Journal of Life Science
2017 Volume.27 No. 12 p.1410 ~ p.1414
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Intersubunit Communication of Escherichia coli Tryptophan Synthase
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Cho Won-Jin
Lim Woon-Ki
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Abstract
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Escherichia coli tryptophan synthase (TS) contains α2β2, which catalyzes the final two steps in Trp biosynthesis. A molecular tunnel exists between the two active sites of α and β subunits in TS. Via intersubunit communication, TS increases catalytic efficiency, including substrate channeling. The β subunit of TS is composed of two domains, one of which, the COMM (communication) domain, plays an important role in intersubunit communication. The α subunit has a TIM barrel structure. This protein has functional regions at the C terminal of β pleated sheets and in its loop regions. Three regions of the α subunit (αL6 [α-loop L6], αL2, and αL3) are implicated in intersubunit communication. In the present study, conformational changes in αL6 were monitored by measuring the sensitivity of mutant proteins in these regions to trypsin. The addition of a α subunit-specific ligand, D,L-α-glycerophosphate (GP), partially restored the sensitivity of mutant proteins to trypsin. In contrast, the addition of the β subunit-specific ligand L-serine (Ser) resulted in varied sensitivity to trypsin, with an increase in PT53 (substitution of Pro with Thr at residue 53) and DG56, decrease in NS104 and wild type, and no change in GD51 and PH53. This finding may be related to several reaction intermediates formed under this condition. The addition of both GP and Ser led to a highly stable state of the complex. The present results are consistent with the current model. The method used herein may be useful for screening residues involved in intersubunit communication.
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KEYWORD
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Intersubunit communication, loop, substrate tunneling, trypsin digestion, tryptophan synthase
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