Identification of the secondary structure of polypeptide chains in solution by x‐ray diffusion scattering

Equilibrium unfolding of the poly(glutamic acid)20 helix

“…[39][40][41][42][43][44][45]60 These structural models are largely based on circular dichroism data but are also supported by FTIR and SAXS measurements. 39,40,[42][43][44][45]60 CD spectra of the E 20 peptide (Figure 2a) are consistent with an a-helical structure at pH 4 and a random coil structure at pH 6. The E 20 helix-coil transition, measured by CD, is also clearly captured by steady state FRET data (Figure 2b).…”

“…42,72 The polyE helix-coil transition has been studied for over 30 years. [39][40][41] Recently, the apparent simplicity of this homopolymer has stimulated the use of polyE as a helix-coil model system for novel experimental and theoretical techniques investigating protein structure and folding kinetics. [42][43][44][45]60 Interestingly, these studies reveal some different new hypotheses regarding the folding mechanism and structure of polyE.…”

“…[35][36][37][38] The helical propensity of polyglutamic acid (polyE) at low pH was established over 30 years ago. [39][40][41] Recently, polyglutamic acid has been used as a model system to study the helix-coil transition owing to the fact that a-helix folding can be initiated from a completely unfolded state using a rapid decrease in pH from 8 to below 5. [42][43][44][45] This has been particularly important in kinetic studies of a-helix folding by CD and FTIR since shifts in pH result in minimal optical perturbation.…”

Inverse Monte Carlo procedure for conformation determination of macromolecules

“…In the first, homopolymers exhibiting helix-coil transitions depending upon pH level (for example, poly-L-lysine and poly-L-glutamic acid 29 ) may be studied using the current methods applied to dilute solution wide-angle X-ray scattering data of Grigoryev et al 30 Similar studies may be performed on carbohydrates or DNA utilizing scattering data and treating sugar or nucleic acid monomers or larger chemical subunits as "residues". Following the approaches of Díaz et al 31 and Svergun et al, 32 the macromolecular structure factor may be obtained by modeling each "residue" as a monomer with an effective scattering intensity equal to the spherically averaged scattering intensity of the entire chemical subunit.…”

X-ray diffuse scattering by proteins in solution. Consideration of solvent influence

“…Actually, a comparison of experimental indicatrices of scattering by an aqueous solution of sperm whale myoglobin (Mb) (Beernan, 1967;Kirste, Schulz & Stuhrmann, 1969;Stuhrmann, 1970;Grigoryev, Volkova & Ptitsyn, 197 Ib) with theoretical curves evaluated on the basis of the known coordinates of atoms (Watson, 1967;Voronin & Fedorov, 1974), shows that beginning with ,-~4 ° (for Cu Kc~ emission) scattering indicatrices become essentially different. In their turn, the recently carried out analysis of theoretical curves of scattering by polypeptide chains in a-helical and t-structural conformations (Voronin & Fedorov, 1972;Voronin, Sarkisov, Kron & Fedorov, 1973) and their comparison with experimental curves (Grigoryev, Volkova & Ptitsyn, 1971a) have revealed considerable discrepancies between theory and experiment in the range of large angles. Naturally, the reason for this divergence is that the theoretical curves pertain to the molecule in vacuum, while the experimental ones pertain to the molecule surrounded by the solvent.…”