The beta bend ribbon, or beta-bend ribbon, is a structural feature in

polypeptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty ...

s and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s. The shortest possible has six

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

residues (numbered ''i'' to ''i+5'') arranged as two overlapping

hydrogen bond In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

ed beta turns in which the

carbonyl In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...

group of residue ''i'' is hydrogen-bonded to the NH of residue ''i+3'' while the carbonyl group of residue ''i+2'' is hydrogen-bonded to the NH of residue ''i+5''. In longer ribbons, this bonding is continued in peptides of 8, 10, etc., amino acid residues. A beta bend ribbon can be regarded as an aberrant

310 helix A 310 helix is a type of secondary structure found in proteins and polypeptides. Of the numerous protein secondary structures present, the 310-helix is the fourth most common type observed; following α-helices, β-sheets and reverse turns. 310 ...

(3/10-helix) that has lost some of its

s. Two websites are available to facilitate finding and examining these features in proteins
Motivated Proteins
an
PDBeMotif
A beta bend ribbon with 12 alanine residues. Colors of atoms: carbon, green; oxygen red; nitrogen blue. The four dashed lines are hydrogen bonds, each of which defines a beta turn.">beta turn">alanine residues. Colors of atoms: carbon, green; oxygen red; nitrogen blue. The four dashed lines are hydrogen bonds, each of which defines a beta turn. The four main types of hydrogen-bonded

beta turn β turns (also β-bends, tight turns, reverse turns, Venkatachalam turns) are the most common form of turns—a type of non-regular secondary structure in proteins that cause a change in direction of the polypeptide chain. They are very common mot ...

s are types I, I’, II and II’. Beta bend ribbons may be formed from any of these types but type I is the commonest in proteins, as it is for single beta turns. Beta bend ribbons made from type I or I’ turns are somewhat twisted, while beta bend ribbons made from type II or II’

s are flat. Beta bend ribbons with mixtures of different beta turn types also occur. Type I beta-bend ribbons regularly occur in

leucine-rich repeat A leucine-rich repeat (LRR) is a protein structural motif that forms an α/β horseshoe tertiary structure, fold. It is composed of repeating 20–30 amino acid stretches that are unusually rich in the hydrophobic amino acid leucine. These Pr ...

s, in the environments sometimes occupied by helices. A protein with a stack of these features is the extracellular ligand-binding domain of the Nogo receptor. Another beta bend ribbon occurs in the

GTPase-activating protein GTPase-activating proteins or GTPase-accelerating proteins (GAPs) are a family of regulatory proteins whose members can bind to activated G proteins and stimulate their GTPase activity, with the result of terminating the signaling event. GAPs are a ...

for Rho in the active, but not the inactive, form of the enzyme. The beta bend ribbon, which incorporates the catalytic

arginine Arginine is the amino acid with the formula (H2N)(HN)CN(H)(CH2)3CH(NH2)CO2H. The molecule features a guanidinium, guanidino group appended to a standard amino acid framework. At physiological pH, the carboxylic acid is deprotonated (−CO2−) a ...

, allows its side-chain guanidino group to approach the active site and enhance

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

activity. Polypeptides consisting of repeats of the dipeptide (α-amino-γ-lactam plus a conventional amino acid) have been shown to adopt a beta bend ribbon conformation.Martin V, Legrand B, Vezenkov LL. Turning peptide sequences into ribbon foldamers by a straightforward multicyclization reaction. Angewandte Chemie 2015;54:1-6.

References

{{reflist, 3 Protein structural motifs