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 trans perpendicular conformation. The other four wells in the tryptophan-59 (chi) ¹ x (chi) ² torsion space minimum perturbation mapping are trans antiperpendicular, gauche⁺ antiperpendicular, gauche⁺ perpendicular, and guache^- perpendicular. The point mutations V33I and V33L are predicted to stabilize the trans 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⁺ antiperpendicular tryptophan-59 conformation. The additional mutation V78A makes a more generous pocket for this conformation. The three mutation A19G, V78G and F80L creates the pocket for the gauche⁺ 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^- 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.

Date Published: 17 August 1994
PDF: 2 pages
Proc. SPIE 2137, Time-Resolved Laser Spectroscopy in Biochemistry IV, (17 August 1994); doi: 10.1117/12.182717

Published in SPIE Proceedings Vol. 2137:
Time-Resolved Laser Spectroscopy in Biochemistry IV
Joseph R. Lakowicz, Editor(s)