β-Bends are stabilizedīy the formation of hydrogen and ionic bonds. Smallest R group, is also frequently found in β-bends. β-Bends are generallyĬomposed of four amino acids, one of which may be proline, the amino acid thatĬauses a kink in the polypeptide chain. They are usually found on the surface of protein molecules and often includeĬharged residues. Hydrogen bonding for peptide bond components within the interior ofĭirection of a polypeptide chain, helping it form a compact, globular shape. The α-helix and β-sheet structures provide maximal [Note: Twisted β-sheets often form the core of Proteins, β-sheets always have a right-handed curl, or twist, when viewed along In this case, the hydrogen bonds are intrachain bonds. A β-sheet canĪlso be formed by a single polypeptide chain folding back on itself (see FigureĢ.7C). Separate polypeptide chains, they are termed interchain bonds. When the hydrogen bonds are formed between the polypeptide backbones of Other (with all the N-termini of the β-strands together as shown in FigureĢ.7C). Or more separate polypeptide chains or segments of polypeptide chains that areĪrranged either antiparallel to each other (with the N-terminal and C-terminalĮnds of the β-strands alternating as shown in Figure 2.7B) or parallel to each Parallel and antiparallel sheets: A β-sheet can be formed from two Perpendicular to the polypeptide backbone in β-sheets (see Figure 2.7A).Ģ. Comparison of a β-sheet and an α-helix: Unlike the α-helix, β-sheets areĬomposed of two or more peptide chains (β-strands), or segments of polypeptideĬhains, which are almost fully extended. A parallel β-sheet formed from a single polypeptide chain folding back on itself.ġ. An antiparallel β-sheet with the β-strands represented as broad arrows. Visualized as broad arrows (Figure 2.7B).įigure 2.7 A. When illustrations are made of protein structure, β-strands are often “pleated,” and these structures are, therefore, often called β-pleated sheets.
Involved in hydrogen bonding (Figure 2.7A). Of the α-helix if they are present in large numbers.įorm of secondary structure in which all of the peptide bond components are Or amino acids, such as valine or isoleucine, that branch at the β-carbon (theįirst carbon in the R group, next to the α-carbon) can interfere with formation Finally, amino acids with bulky side chains, such as tryptophan, Large numbers of chargedĪmino acids (for example, glutamate, aspartate, histidine, lysine, andĪrginine) also disrupt the helix by forming ionic bonds or by electrostatically Which interferes with the smooth, helical structure. Amino acids that disrupt an α-helix: Proline disrupts an α-helixīecause its secondary amino group is not geometrically compatible with the In the primary sequence are spatially close together when folded in theģ. Thus, amino acid residues spaced three or four residues apart Amino acids per turn: Each turn of an α-helix containsģ.6 amino acids. Hydrogen bonds are individually weak, but they collectivelyĢ. Last peptide bond components are linked to each other through intrachain Hydrogen bonds extend up and are parallel to the spiral from the carbonylįour residues ahead in the polypeptide. Hydrogens that are part of the polypeptide backbone (see Figure 2.6). Hydrogen bonds: An α-helix is stabilized byĮxtensive hydrogen bonding between the peptide-bond carbonyl oxygens and amide Myoglobin, whose structure is also highly α-helical, is a globular, flexibleġ. Hair and skin, and their rigidity is determined by the number of disulfideīonds between the constituent polypeptide chains. They are a major component of tissues such as The keratins are a family of closely related, fibrous proteins whose structure A very diverse group of proteins contains α-helices. Outward from the central axis to avoid interfering sterically with each other Is a spiral structure, consisting of a tightly packed, coiled polypeptideīackbone core, with the side chains of the component amino acids extending Polypeptide helices are found in nature, but the α-helix is the most common. [Note: TheĬollagen α-chain helix, another example of secondary structure. The α-helix, β-sheet, and β-bend (β-turn) areĮxamples of secondary structures commonly encountered in proteins. These arrangements are termed the secondary Generally forms regular arrangements of amino acids that are located near each Backbone does not assume a random three-dimensional structure but, instead,
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