Beta sheets

Beta sheets

Beta sheets are a form of secondary structure found in proteins. They consist of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet. A beta strand is a stretch of polypeptide chain typically 3 to 10 amino acids in length with backbone in an extended conformation. Beta sheets include parallel, antiparallel, and mixed forms, distinguished by the relative direction of neighboring strands and the pattern of hydrogen bonding between them.

Structure and Formation

Beta sheets are characterized by their specific hydrogen bonding pattern. In an antiparallel beta sheet, the hydrogen bonds are formed directly between the N-H group of one amino acid and the C=O group of another on an adjacent strand. This results in a more stable and rigid structure. In contrast, parallel beta sheets have hydrogen bonds that are bent and connect the N-H group of one amino acid to the C=O group of an amino acid on the next strand but one over, making them slightly less stable than their antiparallel counterparts. Mixed beta sheets contain regions of both parallel and antiparallel sheets within the same protein.

The side chains of the amino acids in a beta sheet protrude from the sheet alternately above and below the plane of the sheet, allowing for interactions with other molecular entities and contributing to the overall three-dimensional structure of the protein. The specific sequence of amino acids in a beta strand can influence the tendency of the strand to form a sheet, with certain amino acids being more or less conducive to sheet formation.

Function

Beta sheets play a crucial role in the function of many proteins. They provide structural stability and are involved in the formation of protein cores. In some proteins, beta sheets form the majority of the protein structure, contributing to the protein's ability to bind to other molecules, including other proteins, DNA, and ligands. Beta sheets are also involved in the formation of enzyme active sites and can participate in the transmission of neural signals.

Pathology

Misfolding of beta sheets is associated with several diseases, including Alzheimer's disease, Parkinson's disease, and type 2 diabetes. In these conditions, proteins that normally contain beta sheets misfold, leading to the formation of insoluble fibrils that can accumulate in tissues and organs, disrupting normal function.

See Also

• Protein structure
• Alpha helix
• Protein folding
• Molecular biology