A Designed Zn2+-Binding Amphiphilic Polypeptide: Energetic Consequences of -Helicity
详细信息 查看全文
- 作者：David M. Morgan ; David G. Lynn ; Hé ; lè ; ne Miller-Auer ; and Stephen C. Meredith
- 刊名：Biochemistry
- 出版年：2001
- 出版时间：November 20, 2001
- 年：2001
- 卷：40
- 期：46
- 页码：14020 - 14029
- 全文大小：132K
- 年卷期：v.40,no.46(November 20, 2001)
- ISSN：1520-4995
文摘
The 
-helix is a secondary structure with 4.4 amino acids per helical turn. Although it wasproposed in 1952, no experimental support for its existence was obtained until the mid-1980s. Whileshort peptides are unlikely to assume a marginally stable secondary structure spontaneously, they mightdo so in the presence of appropriate structural constraints. In this paper, we describe a peptide that isdesigned to assume a -helical conformation when stabilized by cetyltrimethylammonium bromide (CTAB)micelles and Zn2+. In the designed peptide, lipophilic amino acids are placed such that it would beamphiphilic in the -helical, but not in the 
-helical, conformation. Also, two His residues are incorporatedwith i, i + 5 spacing, designed to allow binding of Zn2+ in a -helical but not an -helical conformation.The peptide was found to form moderately stable monolayers at the air-water interface, with a collapsepressure that almost doubled when there was Zn2+ in the subphase. Also, CTAB micelles induced amarked increase in the helicity of the peptide. In 50% TFE, the peptide had a CD spectrum consistentwith an -helical structure. The addition of 1 mM Zn2+ to this solvent caused a saturable decline inellipticity to approximately half of its original value. The peptide also bound Zn2+ when it was bound toCTAB micelles, with Zn2+ again inducing a decrease in ellipticity. The peptide had slightly greater affinityfor Zn2+ in the presence of the CTAB than in a 50% TFE solution (Kd = 3.1 × 10-4 M in CTAB and 2.3× 10-4 M in TFE). van't Hoff analysis indicated that thermal denaturation of the peptide in 50% TFEcontaining 1 mM Zn2+ was associated with both enthalpic and entropic changes that were greater thanthose in the absence of Zn2+. These observations are all consistent with the proposal that the peptideassumed a -helical conformation in the presence of Zn2+ and CTAB micelles, and has allowed the stabilityof this rare conformation to be assessed.
-helix is a secondary structure with 4.4 amino acids per helical turn. Although it wasproposed in 1952, no experimental support for its existence was obtained until the mid-1980s. Whileshort peptides are unlikely to assume a marginally stable secondary structure spontaneously, they mightdo so in the presence of appropriate structural constraints. In this paper, we describe a peptide that isdesigned to assume a -helical conformation when stabilized by cetyltrimethylammonium bromide (CTAB)micelles and Zn2+. In the designed peptide, lipophilic amino acids are placed such that it would beamphiphilic in the -helical, but not in the -helical, conformation. Also, two His residues are incorporatedwith i, i + 5 spacing, designed to allow binding of Zn2+ in a -helical but not an -helical conformation.The peptide was found to form moderately stable monolayers at the air-water interface, with a collapsepressure that almost doubled when there was Zn2+ in the subphase. Also, CTAB micelles induced amarked increase in the helicity of the peptide. In 50% TFE, the peptide had a CD spectrum consistentwith an -helical structure. The addition of 1 mM Zn2+ to this solvent caused a saturable decline inellipticity to approximately half of its original value. The peptide also bound Zn2+ when it was bound toCTAB micelles, with Zn2+ again inducing a decrease in ellipticity. The peptide had slightly greater affinityfor Zn2+ in the presence of the CTAB than in a 50% TFE solution (Kd = 3.1 × 10-4 M in CTAB and 2.3× 10-4 M in TFE). van't Hoff analysis indicated that thermal denaturation of the peptide in 50% TFEcontaining 1 mM Zn2+ was associated with both enthalpic and entropic changes that were greater thanthose in the absence of Zn2+. These observations are all consistent with the proposal that the peptideassumed a -helical conformation in the presence of Zn2+ and CTAB micelles, and has allowed the stabilityof this rare conformation to be assessed.