Graph Representations of Oxidative Folding Pathways - Essays in Bioinformatics - page 216

Table 2 . Disulfied intermediates experimentally observed in the oxidative folding of
various proteins

Disulfide intermediates 1 Protein Ref.

Bovine pancreatic trypsin inhibitor (BPTI) 3-5; 1-6; 3-5, 1-2;

3-5, 1-4; 3-5, 2-4;
1-6, 2-4; 3-5, 1-6;
1-6, 3-5, 2-4 ;

[24,25]

Insulin-like growth factor (IGF) 2-6; 2-6, 3-5; 2-6, 1-4;

2-6, 4-5; 2-6, 1-3;
2-6, 1-3, 4-5; 1-4, 2-6, 3-5;

[26-28]8]

Epidermal growth factor (EGF) 2-3; 1-2; 4-6; 5-6;

3-4; 2-4, 5-6; 2-5, 3-4;
1-6, 2-5, 3-4; 1-2, 3-4, 5-6;
1-3, 2-4, 5-6;

[29]

1
The intermediates are described with the notation given in Figure 3. The native disulfide connectivity is
given in bold, the fully reduced species is not explicitly included.

BPTI IGF EGF

Figure 6. The oxidative folding pathways of bovine pancreatic trypsin inhibitor
(BPTI), insulin-like growth factor (IGF) and epidermal growth factor (EGF). The
native state is marked by asterisk.

interactions that are specific to the amino acid sequence can guide the initial stages of the
folding process and hence admit a very limited number of disulfide species on the pathway.
Oxidative folding of the fully reduced EGF [29] proceeds through 1-disulfide
intermediates and accumulates rapidly as a single stable 2-disulfide intermediate
(designated as EGF-II), which represents up to more than 85% of the total protein along the
folding pathway. Among the five 1-disulfide intermediates that have been structurally
characterized, only one is native, and nearly all of them are bridges by neighbouring
cysteines. Extensive accumulation of EGF-II indicates that it accounts for the major kinetic
trap of EGF folding. EGF-II contains two of the three native disulfide bonds of EGF,
Cys(14)-Cys(31) and Cys(33)-Cys(42). However, formation of the third native disulfide
(Cys(6)-Cys(20)) for EGF-II is slow and does not occur directly. Kinetic analysis reveals
that an important route for EGF-II to reach the native structure is via rearrangement
pathway through 3-disulfide scrambled isomers. Epidermal growth factor (EGF) [29] forms