Diverse Pathways of Oxidative Folding of Disulfide Proteins: Underlying Causes and Folding Models

Abstract

The pathway of oxidative folding of disulfide proteins exhibits a high degree of diversity, which is manifested mainly by distinct structural heterogeneity and diverse rearrangement pathways of folding intermediates. During the past two decades, the scope of this diversity has widened through studies of more than 30 disulfide-rich proteins by various laboratories. A more comprehensive landscape of the mechanism of protein oxidative folding has emerged. This review will cover three themes. (1) Elaboration of the scope of diversity of disulfide folding pathways, including the two opposite extreme models, represented by bovine pancreatic trypsin inhibitor (BPTI) and hirudin. (2) Demonstration of experimental evidence accounting for the underlying mechanism of the folding diversity. (3) Discussion of the convergence between the extreme models of oxidative folding and models of conventional conformational folding (framework model, hydrophobic collapse model).

Protein folding guides disulfide bond formation

“…The ratio is ∼15, which agrees well with predictions based on polymer theory. The least probable forms about 26 times slower than [5][6][7][8][9][10][11][12][13][14], which is also in rough accord with theory.…”

“…5) of loop formation, PðlÞ ≈ 1 = θ 3 ð1 − expð−l=l 0 ÞÞ, where l is the number of bonds separating two residues, l 0 (roughly, 2-3) is the persistence length of the polypeptide chain, and θ 3 ≈ 2.2 (32). The theory predicts that the ratio of the probability formation of [5][6][7][8][9][10][11][12][13][14] (l = 9) to (l = 24) should be roughly (24/9) θ3 ≈ 9. Based on the theory for loop formation kinetics (33-35), we predict a similar ratio for time scales for forming such contacts.…”

“…From 3,000 trajectories for the type I model, the mean time, τ [5][6][7][8][9][10][11][12][13][14] , for forming the most probable [5][6][7][8][9][10][11][12][13][14] is ≈ 6,000 τ, whereas forms in τ ≈ 8.7 × 10 4 τ (Fig. S8A).…”

“…By arresting the reaction, it is possible to characterize the accumulated intermediates in terms of already formed S-S bonds (10). However, the relationship between protein folding and disulfide bond formation is nontrivial to establish because this requires separate reporters for disulfide bond formation and organization of the rest of the polypeptide chains.…”

Investigating the In Vitro Oxidative Folding Pathways of Bovine Pancreatic Trypsin Inhibitor (BPTI)

“…6,22,23 However, intermediates during conformational folding are difficult to characterize because the folding intermediates are transient and cannot be trapped and isolated. 24 Another limitation of conformational folding is that the denatured protein may contain locally folded structure. [25][26][27][28][29][30][31] As a result, conformational folding studies may only reflect part of the folding pathway.…”