Conformation and Conformational Transitions of Poly-α-Amino Acids in Solution

Lotan, Noah; Berger, Arieh; Katchalski, Ephraim

doi:10.1146/annurev.bi.41.070172.004253

Cited by 56 publications

(18 citation statements)

References 224 publications

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“…It is evident that the peptide is 'randomly' coiled in water. Changing the solvent from buffered water to 1 : 1 v/v water-trifluoroethanol, a structure-promoting solvent [28], induced an a-helix-like CD spectrum exhibiting two negative extrema at 223 nm and 208 nm both with the same amplitude ([O],,, = -3000 k 100") and a crossover at 201 nm. This does not necessarily mean that the peptide actually adopts any a-helical conformation in watertrifluoroethanol; certain types of /3 bend or mixtures of different types of /3 bend can give an a-helix-like CD spectrum [29 -311.…”

Section: I1mentioning

confidence: 99%

Characterization and structural aspects of the enhanced assembly of tubulin after removal of its carboxyl-terminal domain

et al. 1986

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Limited subtilisin cleavage of tubulin results in formation of S-tubulin heterodimer and a 4-kDa carboxylterminal peptide fragment. This carboxyl-terminal domain constitutes an essential site for MAPs interaction and plays a role in modulating the interactions responsible for tubulin self-assembly into microtubules Proc. Natl Acad. Sci. USA 81, 5989; and Biochemistry 23,46751. In the present communication it is shown that addition of the 4-kDa peptide fragment from porcine tubulin to porcine S-tubulin in a molar ratio of about 2: 1 does not affect the assembly of the latter. On the other hand, consistent with previous findings on the binding of the 4-kDa peptide by MAP-2, the peptide inhibited MAP-2-induced tubulin assembly (molar ratio of peptide to tubulin, about 2: 1; peptide to MAP-2, about 30: 1). Comparison of the amino acid composition of the 4-kDa peptide fragment and the C-terminal amino acid residues of S-tubulin with the amino acid sequence of tubulin indicated the subtilisin cleavage site on the tubulin molecule to be between residues G h 4 " and Phe418 of the a-subunit sequence and between Glu407 and Phe4O8 of the B-subunit sequence. The circular dichroism of the 4-kDa fragment in water as solvent is indicative of a molecule with an unordered structure, but when the solvent is changed to a water-trifluoroethanol mixture, the fragment becomes more highly structured.The critical concentration for S-tubulin assembly is not affected by MAPs nor by polylysine, but is decreased by either taxol of dimethylsulfoxide. S-tubulin, with its greater propensity for self-association, has a different conformation from tubulin as shown by a 50% decrease in a-helical content, a more hydrophobic environment of at least some of the tryptophan residues as judged from .fluorimetry, and a greater compaction indicated by flyo = 1.3, as compared to 1.4 for tubulin. The latter point is supported by the observation that the value of the sedimentation coefficient, s20,w = 5.7 S, of the 92-kDa S-tubulin molecule is not significantly different from that of the 100-kDa tubulin, szO,., = 5.8 S.The 100-kDa protein heterodimer tubulin is the subunit protein of microtubules. Tubulin in vitro retains its capacity to self-associate into microtubules, binds nucleotides and interacts with microtubule-associated proteins, MAPs (for reviews see [l -31). Proteolytic dissection of tubulin with several different enzymes has defined structural binding domains for certain small ligands and for MAPs [4--71, revealed accompanying conformational changes resulting from the interactions with these ligands 14, 51 and provided insights into the regulation of tubulin self-association [8]. With respect to tha latter aspect, limited digestion of tubulin with subtilisin results in cleavage at one major site thereby releasing a 4-kDa fragment from the carboxyl-terminal domain of the CI and subunits of tubulin. The cleaved protein heterodimer (S-tubulin), in contrast to tubulin, can self-associate into bundles of microtubules and hooked polymers in the abs...

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Section: I1mentioning

confidence: 99%

Characterization and structural aspects of the enhanced assembly of tubulin after removal of its carboxyl-terminal domain

et al. 1986

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“…The addition of TFE stabilizes ordered structures by promoting intramolecular Hbonding [22], enhancing the helicity of small peptides with inherent helical propensity [23] [24]. The influence of this solvent should, therefore, be to change both the shape of the spectrum and the intensity [25].…”

mentioning

confidence: 99%

The Production ofde novo Folded Proteins by a Stepwise Chain Elongation: A Model for Prebiotic Chemical Evolution of Macromolecular Sequences

Chessari

Thomas

Polticelli

et al. 2006

C&B

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We describe an experimental procedure to mimic the formation of long (over 40 residues) co-oligopetide sequences in many identical copies which may have occurred in the prebiotic molecular evolution. The basic hypothesis is that chain formation is based on the stepwise fragment condensation of randomly generated short oligopeptides, whereby the elongation takes place under the contingent environmental constraints (solubility, pH, salinity), which eliminate most of the products, and thus determine the selection towards one particular small set of chains. The present work aims at verifying the validity of this scheme. In order to do so, we utilize a classic synthetic procedure based on the Merrifield solid-phase synthesis of peptides for the synthesis of randomly produced peptides as well as for their stepwise fragment condensation. Thus, starting from a library of peptides with n=10, the first condensation step produces a library of 16 peptides with 20 residues each (n=20), of which only four remain water-soluble and, therefore, capable to undergo the next fragment condensation step. This gives rise to 16 peptides with n=30, out of which twelve precipitate out under the chosen pH and buffer conditions and are eliminated. Finally, a 44-residue-long water-soluble de novo protein is obtained. This has no homologies or similarities with extant proteins, and, based on circular dichroism (CD), it assumes a stable three-dimensional folding. In agreement with CD data, molecular-modelling simulations suggest an helical fold for the protein with poor, if any, structural homology with known proteins. The implication of this procedure as a general mechanism for the etiology of de novo macromolecular sequences and globular proteins in the origin of life is briefly discussed.

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“…This spectrum is characteristic of polypeptides in an essentially disordered conformation. [9][10][11][12] The CD spectrum of a high-molecular-weight fraction of the polymer (M,. 25,000) in aqueous solution at pH 5.2 is also presented in Fig.…”

Section: Resultsmentioning

confidence: 99%

Conformational changes of poly(L‐histidyl‐L‐alanyl‐α‐L‐glutamic acid) in solution. Transition pathways and conformational intermediates

Goren¹,

Fridkin²,

Katchalski‐Katzir³

et al. 1979

Biopolymers

Self Cite

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SynopsisThe conformation and conformational transitions of poly(His-Ala-Glu) have been investigated by ir, nmr, and CD measurements. The results obtained-as well as the results of our previous investigations by potentiometric titration and hydrodynamic techniques [Goren e t al., Biopolymers (1977) 16,1541-15551-indicate that when dissolved in water, the copolymer assumes a disordered conformation. On changing the pH of the solution, the states of ionization of the side-chain imidazole and carboxyl groups change in the same manner as in low-molecular-weight model compounds. Concomitantly, the overall shape of the macromolecule is altered, while the conformation of the polypeptide backbone changes from one disordered state to another but never assumes a regular form. In water/methanol and waterhrifluoroethanol mixtures, transitions from a disordered state to the a-helix conformation were observed on increasing the alcohol content of the system. The conformational transitions followed pathways which differ from one another according to the experimental conditions employed. Conformational landmarks (intermediates) have been identified along these pathways.

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Conformation and Conformational Transitions of Poly-α-Amino Acids in Solution

Cited by 56 publications

References 224 publications

Characterization and structural aspects of the enhanced assembly of tubulin after removal of its carboxyl-terminal domain

Characterization and structural aspects of the enhanced assembly of tubulin after removal of its carboxyl-terminal domain

The Production ofde novo Folded Proteins by a Stepwise Chain Elongation: A Model for Prebiotic Chemical Evolution of Macromolecular Sequences

Conformational changes of poly(L‐histidyl‐L‐alanyl‐α‐L‐glutamic acid) in solution. Transition pathways and conformational intermediates

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