Structural basis for the impaired channeling and allosteric inter-subunit communication in the beta A169L/beta C170W mutant of tryptophan synthase.

摘要: Abstract We determined the 2.25 A resolution crystal structure of βA169L/βC170W mutant form tryptophan synthase α2β2 complex fromSalmonella typhimurium complexed with α-active site substrate analogue 5-fluoro-indole-propanol-phosphate to identify structural basis for changed kinetic properties (Anderson, K. S., Kim, A. Y., Quillen, J. M., Sayers, E., Yang, X. J., and Miles, E. W. (1995) Biol. Chem. 270, 29936–29944). Comparison wild-type enzyme showed that βTrp170 side chain occludes tunnel connecting α- β-active sites, explaining accumulation intermediate indole during a single turnover. To prevent steric clash between βLeu169 βGly135, located in β-sheet COMM (communication) domain (βGly102-βGly189), latter reorganizes. The conformation results loss hydrogen bonding networks poor activation α-reaction upon formation aminoacrylate at site. 100-fold reduced affinity serine seems result from movement βAsp305 away so it cannot interact hydroxyl group pyridoxal phosphate-bound serine. proposed dissection effects each mutation would explain very different kinetics this βC170F.