| rdfs:comment
| - αシートとは、1951年にライナス・ポーリングとロバート・コリーによって考案された、仮想上のタンパク質の二次構造である。αシートの水素結合のパターンはβシートと類似するが、ペプチド結合のカルボニル基とアミノ基の配向が異なっており、カルボニル基はシートと順方向、アミノ基はシートと逆方向を向いている。そのためαシートは元々電荷を持っていて、カルボニル基の向いている方がマイナス、アミノ基の向いている方がプラスに帯電している。またαヘリックスやβシートなどと異なり、立体配置的にどのアミノ酸でも取れるわけではない。また天然のタンパク質構造中には滅多に見られないが、分子動力学法のシミュレーションによると、アミロイドへの移行の際の中間体となったり、人工設計されたペプチド中で見られたりする。 (ja)
- Alpha sheet (also known as alpha pleated sheet or polar pleated sheet) is an atypical secondary structure in proteins, first proposed by Linus Pauling and Robert Corey in 1951. The hydrogen bonding pattern in an alpha sheet is similar to that of a beta sheet, but the orientation of the carbonyl and amino groups in the peptide bond units is distinctive; in a single strand, all the carbonyl groups are oriented in the same direction on one side of the pleat, and all the amino groups are oriented in the same direction on the opposite side of the sheet. Thus the alpha sheet accumulates an inherent separation of electrostatic charge, with one edge of the sheet exposing negatively charged carbonyl groups and the opposite edge exposing positively charged amino groups. Unlike the alpha helix and be (en)
- La lámina alfa es una estructura secundaria hipotética de proteínas, la cual fue propuesta por vez primera por Linus Pauling y en 1951. El patrón de puentes de hidrógeno en una lámina alfa es similar al de una lámina beta, pero la orientación de los grupos carbonilo y amino en el enlace peptídico es diferente; en una lámina alfa aislada, todos los grupos carbonilo están orientados en la misma dirección de un lado del plegamiento, y todos los grupos amino se encuentran orientados en la misma posición pero del lado opuesto de la lámina. Por lo tanto, la lámina alfa acumula una inherente separación de , con un borde de la lámina exponiendo los grupos carbonilo de carga negativa y el borde opuesto exponiendo los grupos de amino cargados positivamente. A diferencia de la hélice alfa y la lá (es)
- Un feuillet α est une structure secondaire atypique des protéines proposée pour la première fois par Linus Pauling et Robert Corey en 1951. La configuration des liaisons hydrogène dans un feuillet α est semblable à celle d'un feuillet β, mais l'orientation des groupes carbonyle et amine dans les liaisons peptidiques est différente : dans un brin donné, tous les groupes carbonyle sont orientés dans le même sens d'un côté du pli tandis que tous les groupes amine sont orientés dans l'autre sens. De cette façon, le feuillet α accumule une séparation inhérente de charges électriques, avec des groupes carbonyle négatifs le long d'un bord du feuillet et des groupes amine chargés positivement le long de l'autre bord. (fr)
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| has abstract
| - Alpha sheet (also known as alpha pleated sheet or polar pleated sheet) is an atypical secondary structure in proteins, first proposed by Linus Pauling and Robert Corey in 1951. The hydrogen bonding pattern in an alpha sheet is similar to that of a beta sheet, but the orientation of the carbonyl and amino groups in the peptide bond units is distinctive; in a single strand, all the carbonyl groups are oriented in the same direction on one side of the pleat, and all the amino groups are oriented in the same direction on the opposite side of the sheet. Thus the alpha sheet accumulates an inherent separation of electrostatic charge, with one edge of the sheet exposing negatively charged carbonyl groups and the opposite edge exposing positively charged amino groups. Unlike the alpha helix and beta sheet, the alpha sheet configuration does not require all component amino acid residues to lie within a single region of dihedral angles; instead, the alpha sheet contains residues of alternating dihedrals in the traditional right-handed (αR) and left-handed (αL) helical regions of Ramachandran space. Although the alpha sheet is only rarely observed in natural protein structures, it has been speculated to play a role in amyloid disease and it was found to be a stable form for amyloidogenic proteins in molecular dynamics simulations. Alpha sheets have also been observed in X-ray crystallography structures of designed peptides. The regular formation of alpha-sheet by unfolded proteins inevitably involves many L amino acid residues readily adopting the alphaL conformation, which appears at first sight to go against textbook chemistry, which is that, of the 20 amino acids, it is glycine that strongly favours this conformation. The conundrum is resolved by realizing that the alphaL region comprises two overlapping areas, here called γL and αL, which should be considered separately. It turns out that, while the γL conformation is adopted, almost exclusively, by glycine, the αL conformation of alpha-sheet is more commonly, or about as commonly, adopted by any of 15 L-amino acids compared to glycine, the exceptions being proline, threonine, valine and isoleucine, which are rare at this conformation. Hence, of the 20 amino acids, 16 readily adopt the αL conformation. (en)
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