Minimum perturbation mapping reveals that five side chain conformations of tryptophan-59 can potentially pack in the hydrophobic core of ribonuclease T1. In the crystallographic structure tryptophan-59 is in the tram perpendicular conformation. The other four wells in the tryptophan-59 x{sup}1×x{sup}2 torsion space minimum perturbation mapping are trans antiperpendicular, gauche{sup}+ antiperpendicular, gauche{sup}+ perpendicular, and gauche{sup}- perpendicular. The point mutations V33I and V33L are predicted to stabilize the tram antiperpendicular over the perpendicular conformation by 1.3 and 0.6 kcal/mol, respectively. The three gauche conformations require the creation of a new pocket within the protein core. The Mutation F80G creates the pocket for the gauche{sup}+ antiperpendicular tryptophan-59 conformation. The additional mutation V78A makes a more generous pocket for this conformation. The three mutations A19G, V78G and F80L create the pocket for the gauche{sup}+ perpendicular conformation. A slightly more generous mutation at residue 80 may be required to fully stabilize this conformation. It does not appear possible to create a pocket that fits the gauche{sup}- perpendicular conformation better than the other two gauche conformations. The expression of ribonuclease-T1 mutants with tryptophan-59 in a gauche conformation probably requires filling in the crystallographic tryptophan-59 pocket. The mutations A22F, V33F, or V67F are all promising possibilities for this purpose.
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