STRUCTURE OF TRIOSEPHOSPHATE ISOMERASE FROM ESCHERICHIA-COLI DETERMINED AT 2.6-ANGSTROM RESOLUTION

The structure of triosephosphate isomerase (TIM) from the organism Esc herichia coli has been determined at a resolution of 2.6 angstrom. The structure was solved by the molecular replacement method, first at 2. 8 angstrom resolution with a crystal grown by the technique of hanging -drop crystallization from a mother liquor containing the transition-s tate analogue 2-phosphoglycolate (2PG). As a search model in the molec ular replacement calculations, the refined structure of TIM from Trypa nosoma brucei, which has a sequence identity of 46% compared to the en zyme from E. coli, was used. An E. coli TIM crystal grown in the absen ce of 2PG, diffracting to 2.6 angstrom resolution, was later obtained by application of the technique of macro-seeding using a seed crystal grown from a mother liquor without 2PG. The final 2.6 angstrom model h as a crystallographic R factor of 11.9%, and agrees well with standard stereochemical parameters. The structure of E. coli TIM suggests the importance of residues which favour helix initiation for the formation of the TIM fold. In addition, TIM from E. coli shows peculiarities in its dimer interface, and in the packing of core residues within the b eta-barrel.