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A polyproline helix is a type of protein secondary structure which occurs in proteins comprising repeating proline residues. [1] A left-handed polyproline II helix (PPII, poly-Pro II, κ-helix [2]) is formed when sequential residues all adopt (φ,ψ) backbone dihedral angles of roughly (-75°, 150°) and have trans isomers of their peptide bonds.
The cyclic structure of proline's side chain locks the angle φ at approximately −65°. [19] Proline acts as a structural disruptor in the middle of regular secondary structure elements such as alpha helices and beta sheets; however, proline is commonly found as the first residue of an alpha helix and also in the edge strands of beta sheets.
If the helix or sheet hydrogen bonding pattern is too short they are designated as T or B, respectively. Other protein secondary structure assignment categories exist (sharp turns, Omega loops, etc.), but they are less frequently used. Secondary structure is defined by hydrogen bonding, so the
Although the function and hierarchical structure of these collagens may vary, they all share the defining structural feature known as the triple helix, [1] where three left handed polyproline II-type (PPII) helices assemble to form a right-handed supercoiled helical motif.
In 1954, Ramachandran & Kartha (13, 14) advanced a structure for the collagen triple helix on the basis of fiber diffraction data. It consists of a triple helix made of the repetitious amino acid sequence glycine-X-Y, where X and Y are frequently proline or hydroxyproline. [2] [3] Collagen folded into a triple helix is known as tropocollagen.
Mung Beans. Of course, baking isn't the only time you might need an egg replacement. “If you're looking for a protein-packed breakfast with a similar texture to scrambled eggs or an omelet, mung ...
USAID delivers billions of dollars in aid to dozens of countries. Shuttering it means wasted food, 'free-for-all' ISIS camps, and less HIV prevention.
If a warm sirocco wind blows on the cheesemaking day, the cheese-transforming magic works even harder. Fancello says it’s because the cheese has a weaker structure, making the fly’s job easier.