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Reversing the typical pH stability profile of the Trp‐cage
Author(s) -
Graham Katherine A.,
Byrne Aimee,
Son Ruth,
Andersen Niels H.
Publication year - 2019
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.23260
Subject(s) - chemistry , salt bridge , cage , helix (gastropod) , folding (dsp implementation) , side chain , crystallography , protein folding , stereochemistry , mutant , biochemistry , organic chemistry , ecology , mathematics , combinatorics , biology , snail , electrical engineering , gene , engineering , polymer
Abstract The Trp‐cage, an 18‐20 residue miniprotein, has emerged as a primary test system for evaluating computational fold prediction and folding rate determination efforts. As it turns out, a number of stabilizing interactions in the Trp‐cage folded state have a strong pH dependence; all prior Trp‐cage mutants have been destabilized under carboxylate‐protonating conditions. Notable among the pH dependent stabilizing interactions within the Trp‐cage are: (1) an Asp as the helix N‐cap, (2) an H‐bonded Asp9/Arg16 salt bridge, (3) an interaction between the chain termini which are in close spatial proximity, and (4) additional side chain interactions with Asp9. In the present study, we have prepared Trp‐cage species that are significantly more stable at pH 2.5 (rather than 7) and quantitated the contribution of each interaction listed above. The Trp‐cage structure remains constant with the pH change. The study has also provided measures of the stabilizing contribution of indole ring shielding from surface exposure and the destabilizing effects of an ionized Asp at the C‐terminus of an α‐helix.