Beta sheet: Difference between revisions

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==Structure, hydrogen bonding and composition==

The <scene name='88/889825/Toxin_1f94/1'>initial scene</scene> shows a protein with two sheets, one composed of four strands and the other of two. Beta strands are characterized by the extended conformation of the main chain (with phi and psi angles in the upper left quadrant of the [[Ramachandran plot]]) and hydrogen bonds to the neighboring strands. Strands are either in <scene name='88/889825/6l26_direction/1'>a parallel or an antiparallel arrangement</scene>, resulting in different hydrogen bonding patterns [https://www.ncbi.nlm.nih.gov/books/NBK22580/#_A328_]. Accordingly, beta sheets are classified as parallel, antiparallel or mixed. The antiparallel arrangement of strands is more prevalent <ref>DOI:10.1021/ci200027d</ref>. The beta strands on the edge of a sheet will have hydrogen bond donors and acceptors that have no other strand to partner with unless the sheet forms a cylindrical structure called a beta barrel, such as in the [[green fluorescent protein]] structure.

The <scene name='88/889825/Toxin_1f94/1'>initial scene</scene> shows a protein with two sheets, one composed of four strands and the other of two. Beta strands are characterized by the extended conformation of the main chain (with phi and psi angles in the upper left quadrant of the [[Ramachandran plot]]) and hydrogen bonds to the neighboring strands. Strands are either in <scene name='88/889825/6l26_direction/1'>a parallel or an antiparallel arrangement</scene>, resulting in different <scene name='88/889825/6l26_direction/2'>hydrogen bonding patterns</scene> [https://www.ncbi.nlm.nih.gov/books/NBK22580/#_A328_]. Accordingly, beta sheets are classified as parallel, antiparallel or mixed. The antiparallel arrangement of strands is more prevalent <ref>DOI:10.1021/ci200027d</ref>. The beta strands on the edge of a sheet will have hydrogen bond donors and acceptors that have no other strand to partner with unless the sheet forms a cylindrical structure called a beta barrel, such as in the [[green fluorescent protein]] structure.

The side chains of amino acids in a beta sheet point outward on either side of the sheet, with alternate side chains in a strand pointing in opposite directions. The side chains of beta sheets are often in contact with side chains of other secondary structure elements connecting the strands, forming a hydrophobic core on either side of the sheet. This explains why many amino acids in sheets are hydrophobic. Just as for alpha helices, proline and glycine residues are uncommon. Proline lacks the hydrogen donor present in the peptide group, and glycine has more conformational states than all the other amino acids. Different from alpha helices, beta sheets are able to accomodate beta-branched side chains such as valine and isoleucine, so these are more prevalent in beta sheets than in alpha helices.

Beta sheet: Difference between revisions

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 <StructureSection load='' size='350' side='right' caption='' scene='88/889825/Toxin_1f94/1'>
 ==Structure, hydrogen bonding and composition==
-The <scene name='88/889825/Toxin_1f94/1'>initial scene</scene> shows a protein with two sheets, one composed of four strands and the other of two. Beta strands are characterized by the extended conformation of the main chain (with phi and psi angles in the upper left quadrant of the [[Ramachandran plot]]) and hydrogen bonds to the neighboring strands. Strands are either in <scene name='88/889825/6l26_direction/1'>a parallel or an antiparallel arrangement</scene>, resulting in different hydrogen bonding patterns [https://www.ncbi.nlm.nih.gov/books/NBK22580/#_A328_]. Accordingly, beta sheets are classified as parallel, antiparallel or mixed. The antiparallel arrangement of strands is more prevalent <ref>DOI:10.1021/ci200027d</ref>.  The beta strands on the edge of a sheet will have hydrogen bond donors and acceptors that have no other strand to partner with unless the sheet forms a cylindrical structure called a beta barrel, such as in the [[green fluorescent protein]] structure.
+The <scene name='88/889825/Toxin_1f94/1'>initial scene</scene> shows a protein with two sheets, one composed of four strands and the other of two. Beta strands are characterized by the extended conformation of the main chain (with phi and psi angles in the upper left quadrant of the [[Ramachandran plot]]) and hydrogen bonds to the neighboring strands. Strands are either in <scene name='88/889825/6l26_direction/1'>a parallel or an antiparallel arrangement</scene>, resulting in different <scene name='88/889825/6l26_direction/2'>hydrogen bonding patterns</scene> [https://www.ncbi.nlm.nih.gov/books/NBK22580/#_A328_]. Accordingly, beta sheets are classified as parallel, antiparallel or mixed. The antiparallel arrangement of strands is more prevalent <ref>DOI:10.1021/ci200027d</ref>.  The beta strands on the edge of a sheet will have hydrogen bond donors and acceptors that have no other strand to partner with unless the sheet forms a cylindrical structure called a beta barrel, such as in the [[green fluorescent protein]] structure.
 The side chains of amino acids in a beta sheet point outward on either side of the sheet, with alternate side chains in a strand pointing in opposite directions. The side chains of beta sheets are often in contact with side chains of other secondary structure elements connecting the strands, forming a hydrophobic core on either side of the sheet. This explains why many amino acids in sheets are hydrophobic. Just as for alpha helices, proline and glycine residues are uncommon. Proline lacks the hydrogen donor present in the peptide group, and glycine has more conformational states than all the other amino acids. Different from alpha helices, beta sheets are able to accomodate beta-branched side chains such as valine and isoleucine, so these are more prevalent in beta sheets than in alpha helices.