Guanidinium-induced denaturation by breaking of salt bridges

Despite its wide use as a denaturant, the mechanism by which guanidinium (Gdm⁺) induces protein unfolding remains largely unclear. Herein, we show evidence that Gdm⁺ can induce denaturation by disrupting salt bridges that stabilize the folded conformation. We study the Gdm⁺-​induced denaturation of a series of peptides contg. Arg​/Glu and Lys​/Glu salt bridges that either stabilize or destabilize the folded conformation. The peptides contg. stabilizing salt bridges are found to be denatured much more efficiently by Gdm+ than the peptides contg. destabilizing salt bridges. Complementary 2D-​IR measurements suggest a denaturation mechanism in which Gdm⁺ binds to side-​chain carboxylate groups involved in salt bridges.