Native-like β-hairpin structure in an isolated fragment from ferredoxin: NMR and CD studies of solvent effects on the N-terminal 20 residues

Abstract

The conformational properties of protein fragments have been widely studied as models of the earliest initiation events in protein folding. While native-like alpha-helices and beta-turns have been identified, less is known about the factors that underly beta-sheet formation, in particular beta-hairpins, where considerably greater long-range order is required. The N-terminal 20 residue sequence of native ferredoxin I (from the blue-green alga Aphanothece sacrum) forms a beta-hairpin in the native structure and has been studied in isolation by NMR and CD spectroscopy. Local native-like interactions alone are unable to stabilize significantly a folded conformation of the 20-residue fragment in purely aqueous solution. However, we show that the addition of low levels of organic co-solvents promotes formation of native-like beta-hairpin structure. The results suggest an intrinsic propensity of the peptide to form a native-like beta-hairpin structure, and that the organic co-solvent acts in lieu of the stabilizing influence of tertiary interactions (probably hydrophobic contacts) which occur in the folding of the complete ferredoxin sequence. The structure of the isolated hairpin, including the native-like register of interstrand hydrogen bonding interactions, appears to be determined entirely by the amino acid sequence. The solvent conditions employed have enabled this intrinsic property to be established.

Natural polypeptide scaffolds: β‐sheets, β‐turns, and β‐hairpins

“…They also are structures found in many naturally occurring bioactive cyclic peptides such as gramicidin S and the peptide hormones oxytocin and vasopressin. Importantly, several studies have demonstrated the stability of an isolated -hairpin [21][22][23][24][25][26][27][28] and, from these studies, considerable insight has been obtained into the factors that contribute to the conformational energetics. Cross-strand interactions are key and may include aromatic-aromatic, 29 charge-charge electrostatic, 30 or hydrophobic packing interactions.…”

Cross-Strand Coupling and Site-Specific Unfolding Thermodynamics of a Trpzip β-Hairpin Peptide Using 13C Isotopic Labeling and IR Spectroscopy

“…Studies of isolated, water-soluble -hairpins can provide valuable insight into properties of -sheet structure and folding since -hairpins are considered to act as possible nucleation sites for protein folding. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Additionally, their detailed structural interactions can be relevant in developing an understanding of the mechanism for forming various -sheet structures such as found in many (amyloid-like) neurodegenerative diseases in which protein aggregation is an important pathology. [15][16][17][18] During the past decade, there have been many reports discussing de novo designed, water-soluble -hairpin peptide systems, as well documented in several reviews.…”

De novo design of a monomeric three‐stranded antiparallel β‐sheet

“…In spite of this, some linear peptides have recently been shown to fold into monomeric b-hairpins in aqueous solutioñ Blanco et al, 1998;Maynard et al, 1998;Smith & Regan, 1997! or alcohol-water mixtures~Cox et al, 1993Blanco et al, 1994;Searle et al, 1996!. Furthermore, the design and structure elucidation of model b-hairpins has demonstrated that the conformation of the turn plays a key role in directing b-hairpin structure~de Alba et al, 1996Alba et al, , 1997aHaque & Gellman, 1997!.…”