Structure of Poly-L-Proline

Cowan, P.; McGavin, Stewart

doi:10.1038/176501a0

Cited by 438 publications

(286 citation statements)

References 7 publications

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“…Changes in the ellipticity at this maximum that generate an isodichroic value are interpreted to indicate a change in the fractional population of residues in the PII conformation. This fractional population is de- Presence of PII conformations in the proline 9 guest peptide A PI1 conformation is a left-handed extended helix first described for all-trans polyproline (Cowan & McGavin, 1955;Sasisekharan, 1959). Each residue in a PI1 conformation has 4, T angles of about -80" and + 150".…”

Section: Discussionmentioning

confidence: 99%

The role of PII conformations in the calculation of peptide fractional helix content

1997

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Changes in the temperature, pH, ionic strength, or denaturant concentration of aqueous solutions of the monomeric non-a-helical peptide acetylYEAAAKEAPAKEAAAKAamide generate changes in its dichroic spectrum characteristic for a conformational transition. This transition has the characteristic features of a residue PII/unstructured conformational equilibrium in which PII denotes an extended left-handed helical conformation and unstructured denotes all the remaining conformations in a random coil ensemble. Replacement of the proline residue facilitates population of residues in an a-helical conformation. However, the elliptcity values for these non-proline peptides merge with the ellipticity of the proline peptide as the population of residues in the a-helix conformation is diminished. This convergence suggests that all residues in a host/guest peptide series of the same length share a common PII/unstructured conformational equilibrium in a given solvent. We propose that the fractional helix content of peptides within such a series may be estimated by using a two-state calculation in which the ellipticity for the non-a-helix conformations is provided by a peptide having a central proline guest residue.Keywords: ellipticity; helix content; peptide; PI1 conformation; random coil A variety of studies has examined the effect of a guest amino acid residue on the helical content of a host peptide of defined sequence (e.g., O'Neil & DeGrado, 1990;Lyu et al., 1990Lyu et al., , 1993Forood et al., 1993;Park et al., 1993; Chakrabarrty et al., 1994;Doig & Baldwin, 1995;Munoz et al., 1995). Such studies have been used to rank order the apparent helix propensity of the 20 common amino acid residues and to generate residue statistical parameters for prediction of helical content from sequence.We have utilized the sequence acetylYEAAAKEAXAKEAA AKAamide to synthesize a series of host/guest peptides, each containing a different guest residue X at sequence position 9 (Merutka et al., 1990;Park et al., 1993). These host/guest peptides generate a nested set of dichroic spectra having an isodichroic point at 203 nm and -16,500 deg cm2 dmol" at pH 7 and 0". The alanine 9 guest peptide has the most negative ellipticity at 222 nm, -24,300 deg cm2 d m o l~ I , and a dichroic spectrum characteristic for peptide solutions having a high fractional population of residues in the helical conformation. The proline 9 guest peptide has the least negative ellipticity at 222 nm, +I20 deg cmz dmol", and a dichroic spectrum characteristic for a random coil conformation.The proline 9 guest peptide was used subsequently to measure the effects of a variety of denaturing solvent conditions on the dichroic spectrum of a random coil. We were surprised to observe Reprint requests to: Earle Stellwagen, Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242; e-mail: cmdste@blue.weeg. uiowa.edu. that these solvent conditions generated a nested set of dichroic spectra characteristic for a conformational transition. We suggest that these dic...

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Section: Discussionmentioning

confidence: 99%

The role of PII conformations in the calculation of peptide fractional helix content

1997

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“…In the 1950s, elucidation of the structural features of polyproline 1 and polyglycine 2 provided a conceptual framework for the proposal of the triple-helical structure of collagen and insight into its basic stabilizing interactions. The collagen triplehelix structure, as proposed by Ramachandran and Kartha (1955), 3 Rich and Crick (1955), 4 and Cowan et al (1955), 5 consists of three polypeptide chains, each in a polyproline II-like (PPII) conformation, supercoiled around a common axis.…”

Section: Introductionmentioning

confidence: 99%

Triple‐helical peptides: An approach to collagen conformation, stability, and self‐association

et al. 2008

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Peptides have been an integral part of the collagen triple‐helix structure story, and have continued to serve as useful models for biophysical studies and for establishing biologically important sequence‐structure‐function relationships. High resolution structures of triple‐helical peptides have confirmed the basic Ramachandran triple‐helix model and provided new insights into the hydration, hydrogen bonding, and sequence dependent helical parameters in collagen. The dependence of collagen triple‐helix stability on the residues in its (Gly‐X‐Y)n repeating sequence has been investigated by measuring melting temperatures of host‐guest peptides and an on‐line collagen stability calculator is now available. Although the presence of Gly as every third residue is essential for an undistorted structure, interruptions in the repeating (Gly‐X‐Y)n amino acid sequence pattern are found in the triple‐helical domains of all nonfibrillar collagens, and are likely to play a role in collagen binding and degradation. Peptide models indicate that small interruptions can be incorporated into a rod‐like triple‐helix with a highly localized effect, which perturbs hydrogen bonds and places the standard triple‐helices on both ends out of register. In contrast to natural interruptions, missense mutations which replace one Gly in a triple‐helix domain by a larger residue have pathological consequences, and studies on peptides containing such Gly substitutions clarify their effect on conformation, stability, and folding. Recent studies suggest peptides may also be useful in defining the basic principles of collagen self‐association to the supramolecular structures found in tissues. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 345–353, 2008.This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com

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“…PPII is a rather regular structural motif in that it exhibits a perfect, left-handed threefold rotational symmetry (3 1 -helix) for its canonical conformation, with ( , ) ϭ (Ϫ78°, 146°) (14). Woody and coworkers (15)(16)(17) have published a series of papers proving that PPII gives rise to a far UV-ECD spectrum, which many in the scientific community still interpret as indicative of random coil (15).…”

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confidence: 99%

The alanine-rich XAO peptide adopts a heterogeneous population, including turn-like and polyproline II conformations

Schweitzer‐Stenner

Measey

2007

Proc. Natl. Acad. Sci. U.S.A.

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The solution structure of the hepta-alanine polypeptide Ac-X 2A7O2-NH2 (XAO) has been a matter of controversy in the current literature. On one side of the argument is a claim that the peptide adopts a mostly polyproline II ( We have used an excitonic coupling model to simulate the amide I band of the FTIR, vibrational circular dichroism, and isotropic and anisotropic Raman spectra of XAO, where, for each residue, the backbone dihedral angle was constrained by using the reported 3 JC␣HNH values and a modified Karplus relation. The best reproduction of the experimental data could only be achieved by assuming an ensemble of conformations, which contains various ␤-turn conformations (Ϸ26%), in addition to ␤-strand (Ϸ23%) and PPII (Ϸ50%) conformations. PPII is the dominant conformation in segments not involved in turn formations. Most of the residues were found to sample the bridge region connecting the PPII and right-handed helix troughs in the Ramachandran plot, which is part of the very heterogeneous ensemble of conformations generally termed type IV ␤-turn.alanine propensity ͉ amide I ͉ unfolded peptides ͉ vibrational spectroscopy T he unfolded state of peptides and proteins has been the subject of an increasing number of experimental and theoretical studies (1-9), owing to the discovery of naturally disordered, although biologically functioning, proteins and peptides (9), and the general relevance for a thorough understanding of the protein folding process. In this context, the possible existence of local residue structure would certainly affect the initial phase of the folding process (10). The existence of such locally ordered segments has first been proposed by Tiffany and Krimm (11) based on electronic circular dichroism (ECD) measurements on poly-L-proline, poly-L-lysine, and poly-L-glutamic acid. They concluded that charged polypeptides assume, at least locally, a rather ordered polyproline II (PPII) conformation, which is the structure adopted by trans-poly-L-proline. This notion was later confirmed by vibrational circular dichroism (VCD) studies on a variety of unfolded polypeptides and proteins (12,13).PPII is a rather regular structural motif in that it exhibits a perfect, left-handed threefold rotational symmetry (3 1 -helix) for its canonical conformation, with ( , ) ϭ (Ϫ78°, 146°) (14). Woody and coworkers (15-17) have published a series of papers proving that PPII gives rise to a far UV-ECD spectrum, which many in the scientific community still interpret as indicative of random coil (15). Recently, they reported a very convincing quantitative agreement between the PPII content of ␤II proteins, derived from crystallographic data, and ECD spectra (16). The PPII signal was also observed in the spectrum of the unfolded state of many proteins subjected to denaturing detergents (17). Thermal denaturation, however, often yields a conformation that is reflected by a weak, nearly symmetric, couplet with a positive maximum between 180 and 210 nm and a negative minimum between 210 and 230 nm (11,16,18). ECD ...

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Structure of Poly-L-Proline

Cited by 438 publications

References 7 publications

The role of PII conformations in the calculation of peptide fractional helix content

The role of PII conformations in the calculation of peptide fractional helix content

Triple‐helical peptides: An approach to collagen conformation, stability, and self‐association

The alanine-rich XAO peptide adopts a heterogeneous population, including turn-like and polyproline II conformations

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