CHEMISTRY, BIOPHYSICS. For the article “Interplay among side chain sequence, backbone composition, and residue rigidification in polypeptide folding and assembly,” by W. Seth Horne, Joshua L. Price, and Samuel H. Gellman, which appeared in issue 27, July 8, 2008, of Proc Natl Acad Sci USA (105:9151–9156; first published June 27, 2008; 10.1073/pnas.0801135105), the authors note that the circular dichroism (CD) and analytical ultracentrifugation (AU) data reported in Fig. 3 and Table 1 for oligomer 8 were inadvertently obtained for a point mutant in which β3-hIle12 was substituted with α-Ile. The authors have subsequently prepared and characterized an authentic sample of α/β-peptide 8. The authors state: “The folding and self-assembly of authentic 8 is qualitatively similar to that of the point mutant, although the quaternary structural stability of 8 is somewhat lower. Authentic 8 shows greater quaternary structural stability than does 5, and this improvement was the most important feature of 8 with respect to the main thesis of the article. Therefore, this error does not affect the conclusions of the article.” The corrected figure and its legend, and the corrected table, appear below.
Fig. 3.
CD spectra of 1–9. (A) CD spectra for GCN4-pLI α-peptide 1 and α/β-peptides 2–6 generated from simple α → β3 substitution. (B) CD spectra for GCN4-pLI α/β-peptide derivatives bearing cyclic β-residues. The colors of the spectra in B match the corresponding acyclic β-residue derivatives in A. All spectra were acquired for 100 μM α-peptide or α/β-peptide in 10 mM NaOAc (pH 4.6).
Table 1.
Summary of CD and AU data for 1–9
| Peptide | Backbone pattern | Cyclic β-residues | [θ]min, deg cm2 dmol−1 res−1* |
Tm, °C† |
Nassoc‡ | |
|---|---|---|---|---|---|---|
| 100 μM | 25 μM | |||||
| 1 | (α) | − | −30,000 | >100 | n.d. | 4 |
| 2 | (ααβαααβ) | − | −39,000 | >100 | >100 | 3 |
| 3 | (αααβ) | − | −34,000 | 77 | 63 | 4 |
| 4 | (ααβ) | − | −42,000 | 82 | 73 | 4 |
| 5 | (ααβαβαβ) | − | −22,000 | 44 | – | (1, 3) |
| 6 | (αβ) | − | −5,000 | – | – | n.d. |
| 7 | (ααβ) | + | −41,000 | >100 | >100 | 4 |
| 8 | (ααβαβαβ) | + | −31,000 | 82 | 67 | (1, 4)§ |
| 9 | (αβ) | + | −30,000 | 80 | 70 | (1, 5) |
*Minimum molar ellipticity observed in the CD spectrum of a 100 μM sample in 10 mM NaOAc (pH 4.6) at 25°C.
†Thermal unfolding transitions observed by CD of peptide at the indicated concentration in 10 mM NaOAc (pH 4.6).
‡Apparent association state determined by AU of a 200 μM sample in 10 mM NaOAc (pH 4.6), 150 mM NaCl; numbers in parentheses indicate a mixture of two species.
§Data acquired for a 100 μM sample in 10 mM NaOAc (pH 4.6); higher concentration and the addition of 150 mM NaCl led to aggregation.