Table IV.
The Effects of Trp to Tyr Mutations
| Sequence | Turn G | Hairpin | CSD (ppm) | ||||
|---|---|---|---|---|---|---|---|
| WP analogs | δΔHα | fHP based on <CSD> | S-2 W/Y Hε3/Hδ | S-2 Hβ3 | S+2 W/Y Hε/Hδ | S+2 Hβ3 | S+4 HNE |
| Ac-WIpGKWTG-NH2 | n. a. | 0.95±0.03 a | -0.38 | -0.15 | -1.87 | -1.44 | -3.07 |
| Ac-YIpGKWTG-NH2 | n. a. | 0.62±0.06 a | -0.11 c | -0.31 c | -0.89 | -0.26 | -1.93 |
| Ac-WIpGKYTG-NH2 | n. a. | 0.86±0.05 a | -0.21 | -0.20 | -1.05 c | -1.79 c | -1.78 |
| HP6V analogs | |||||||
| KAVWINGKWTVE | 0.589 | 0.85 b | -1.922 | -1.54 | -0.280 | -0.26 | +0.55 |
| KAVYINGKWTVE | 0.504 | ≈ 0.76 b | -1.324 c,d | -2.05c | -0.240 | -0.14 | +0.55 |
| KAVWINGKYTVE | 0.445 | ≈ 0.33 b | -0.702 | -0.14 | -0.562 c | -0.95 c | +0.23 |
Fraction folded estimates for the WP peptide analogs are based on the fractional CSDs observed for the applicable subset of the 1/2/5/6α and 2/6N backbone sites.
CSDs used for (Y2A,S5I)-HP6V series were those for the 2α, 11α, 3N, 8N, and 10N sites. Due to changes in ring current effects these are viewed as approximate values.
When the edge aryl is tyrosine, the beta proton shifts are expected to be proportionally greater than delta proton shifts. This is due to the averaging of the two δ sites, only one of which can be close to and in the shielding cone of the indole ring.
The 1.32 ppm ring current shift for the averaged Tyr Hδ’s is remarkably large. It is accompanied by a very large upfield shift for one the Tyr Hβ resonances (Hβ3). These values in themselves imply a large folded population.