Roles of Hydrogen Bonding Residues in the Interaction between the α and β Subunits in the Tryptophan Synthase Complex

摘要: The interaction of the alpha subunit with beta2 tryptophan synthase is known to be necessary for activation each and catalytic efficiency alpha2beta2 complex. To elucidate roles hydrogen bonds in site between beta subunits association, eight mutant at five bonding residues (N104D, N104A, N108D, N108A, E134A, E135A, N157D, N157A) were constructed, thermodynamic parameters association obtained using a titration calorimeter. N104D N104A mutations remarkably decreased stimulation activities, constants, enthalpies. Although constant activities E134A reduced absence salt, change enthalpy was relatively small, addition salt could repair its defects. substitutions positions 135 157 did not affect activity Gibbs energy corresponding defect 1 mol bond. present results suggest that which has mutation position 104 cannot fold into an intact conformation upon complex formation, resulting activities. bond Asn-104, conserved residue among 16 microorganisms, especially important alpha/beta mutual activation.