Beta pleated sheet (secondary structure of proteins)

Secondary structure of protein: Beta pleated sheet

Shape: Sheet like structure.

The sheet conformation consists of pairs of strands lying side-by-side.

Formation: Beta sheets are formed by linking two or more beta strands by H bonds.

Bonds: Hydrogen bonds are formed in between the neighboring N-H and C=O groups of adjacent peptide chains. It provide stability to beta sheets.

The carbonyl oxygens of aminoacid in one strand hydrogen bond with the amino hydrogen on the aminoacid of the adjacent strand.

The hydrogen bonding in a ß-sheet is between strands (inter-strand) rather than within strands (intra-strand).

R group orientation: -R groups are directed to both inside and outside of the sheet.

Number of strands: This cannot exist as a single beta strand; there are must be two or more.

Types: This can be parallel, anti-parallel or mixed.

The two strands can be either parallel or anti-parallel depending on whether the strand directions (N-terminus to C-terminus) are the same or opposite.

If the strands are oriented such that the N  → C directions are the same, the sheet is called a parallel β sheet

If the strands are oriented such that the N  → C directions are opposite, the sheet is called a anti parallel β sheet

The anti-parallel ß-sheet is more stable due to the more well-aligned hydrogen bonds.

Location in protein: β sheets are usually found in the interior of the protein.

Qualities (parameters): 3.5 Ao rise between residues.

 

Anti parallel beta sheet

 

Parallel beta sheet

Aminoacid preference: Beta sheet prefers Tyr, Trp, (Phe, Met), Ile, Val, Thr, Cys.

Amino acids such as tryptophan, tyrosine, and phenylalanine , are often found in β pleated sheets (large ring structures in their R groups ). Because the β pleated sheet structure provides plenty of space for the side chains.

The aminoacid residues of a β sheet, when viewed edge-on, form a zigzag or pleated pattern in which the R groups of adjacent residues point in opposite directions.

Unlike the compact backbone of the α helix, the peptide backbone of the ß sheet is highly extended.

Strong sheet formers (Hb): Val, Ile, Tyr

Strong sheet breakers (Bb): Asp, Glu, Pro

 

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