Context-Dependent Effects of Asparagine Glycosylation on Pin WW Folding Kinetics and Thermodynamics

Abstract

In extracting folding and unfolding rate information from our apparent rate constant data, and in fitting the extracted folding rates as a function of temperature to Kramer's model, we inadvertently used the pre-jump equilibrium temperature instead of the post-jump temperature: a difference of 12 °C. The absolute folding and unfolding rate values for each WW variant in Tables 3 and ​and44 are different than reported in the original paper by 2-fold, but most of the folding and unfolding rate ratios (comparing the folding or unfolding rates of the glycosylated vs. non-glycosylated WW variants) are similar to the values presented in the original paper. The changes to the data do not change the conclusion of our paper that specific, evolved protein-glycan contacts must also play a role in mediating the beneficial energetic effects on protein folding that glycosylation can confer. Table 3 Experimentally Measured and Computationally Predicted Folding Rates for Pin WW Variants Having Either Asn or Asn-GlcNAc at the Indicated Positionsa Table 4 Experimentally Measured and Computationally Predicted Unfolding Rates for Pin WW Variants Having Either Asn or Asn-GlcNAc at the Indicated Positionsa The corrected data appear in Tables 3 and ​and44 below. The corrected versions of Figures S44 to S55 (the data that Tables 3 and ​and44 summarize) are provided in the Supporting Information. The following sentences in the Results section text referring to our kinetic data (pp. 15364): The modest stabilizing effect of the Asn to Asn-GlcNAc substitution at positions 20 and 30 appears to be a result, in part, of an increased folding rate. Glycosylation at position 20 (compare 20 with 20g) increases the folding rate ⍰1.1-fold (Table 3). Glycosylation at position 30 (compare 30 with 30g) has a similar effect. These small folding rate increases agree with the predictions of the computational model and could be consistent with a small amount of denatured-state destabilization as a consequence of glycosylation. However, the decreased unfolding rate of 20g relative to 20 (also predicted by the model) could indicate that glycosylation at position 20 actually stabilizes the folding transition state and native state simultaneously. are changed to: The modest stabilizing effect of the Asn to Asn-GlcNAc substitution at position 20 appears to be primarily due to an increased folding rate (20g folds 1.5 times faster than 20). This folding rate increase agrees with the predictions of the computational model, and could be consistent with a small amount of denatured-state destabilization as a consequence of glycosylation. However, the unfolding rates of 20g and 20 are indistinguishable, which disagrees with the predicted decrease in unfolding rate upon glycosylation. The stabilizing effect of glycosylation at position 30 appears to come primarily from a decrease in unfolding rate (30g unfolds 0.7 times as fast as non-glycosylated Pin WW), as predicted by the model. This decrease compensates for an unexpected decrease in folding rate: 30g folds 0.8 times as fast as Pin WW whereas the model predicted a large increase in folding rate. Results for 33 and 33g are similarly inconsistent with the predictions of the model. In addition, the following sentence in the Discussion section text about our kinetic data (pp. 15366): For example, the observed increased stability and increased folding rate of 20g relative to 20, and of 30g relative to 30, could be the result of simultaneous transition state and native state stabilization (rather than destabilization of the denatured ensemble), reflecting the presence of favorable glycan-protein contacts at these positions. is changed to: For example, the observed increased stability of 20g and 30g relative to 20 and 30, respectively, could be the result of favorable native-state GlcNAc-protein contacts at these positions.