Allosteric regulation of substrate channeling and catalysis in the tryptophan synthase bienzyme complex

作者：Dunn Michael F^*

来源：Archives of Biochemistry and Biophysics, 2012, 519(2): 154-166.

DOI：10.1016/j.abb.2012.01.016

• Allostery
• Substrate channeling
• Tryptophan synthase

The tryptophan synthase alpha(2)beta(2) bi-enzyme complex catalyzes the last two steps in the synthesis of L-tryptophan (L-Trp). The alpha-subunit catalyzes cleavage of 3-indole-D-glycerol 3%26apos;-phosphate (IGP) to give indole and D-glyceraldehyde 3%26apos;-phosphate (G3P). Indole is then transferred (channeled) via an interconnecting 25 A-long tunnel, from the alpha-subunit to the beta-subunit where it reacts with L-Ser in a pyridoxal 5%26apos;-phosphate-dependent reaction to give L-Trp and a water molecule. The efficient utilization of IGP and L-Ser by tryptophan synthase to synthesize L-Trp utilizes a system of allosteric interactions that (1) function to switch the alpha-site on and off at different stages of the beta-subunit catalytic cycle, and (2) prevent the escape of the channeled intermediate, indole, from the confines of the alpha- and beta-catalytic sites and the interconnecting tunnel. This review discusses in detail the chemical origins of the allosteric interactions responsible both for switching the alpha-site on and off, and for triggering the conformational changes between open and closed states which prevent the escape of indole from the bienzyme complex.

• 出版日期2012-3-15