Sheets in Proteins
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A β-pleated sheet contains multiple peptide strands that are positioned adjacent to one another as the one shown on the right[1]. The planes of the are formed by the planes of the peptide bond. The alpha carbons of the peptide chain are at the valleys and peaks of the pleats. The peptides are (blue amino end changing to red carboxy end) to show that the adjacent peptides are running in opposite directions making the sheet antiparallel. Another way of detecting the is by displaying as cartoon. The adjacent chains align so that are formed between the imino hydrogens of one chain and the carbonyl oxygens of an adjacent chain. These hydrogen bonds provide the major attractive force which maintains the sheet structure. Psi and phi values that permit this alignment in antiparallel sheets have of +1350 and -1390, respectively. The median values for a parallel sheet are +1130 and -1190.
Twisted sheets are found in globular proteins. Unlike the of sheets the valleys and the peaks of a [2] do not fall on parallel lines. Observe that the sheet is , and showing . Notice that in contrast to the hydrogen bonds of the antiparallel sheet shown above where the bonds were parallel here the bonds are diagonal to each other. Show for randomly chosen residues. There are a wide range of values for both psi and phi, +96 to +148 and -108 to -142, respectively. Sheet shown in the context of of glycogen phosphorylase. Examples of [3]. Showing only the , and with . Show the of values for psi and phi for randomly chosen residues to be +90 to +167 and -98 to -178, respectively. These ranges overlap the values for the twisted parallel showing that there is no difference in the values for the two types of twisted sheets. Median values for psi and phi are +1400 and -1250, respectively, regardless if of parallel or antiparallel.
Notes and ReferencesNotes and References
- ↑ This model was hand constructed using HyperChem and setting all psi and phi values to 1350 and -1390, respectively.
- ↑ This sheet is part of the structure of domain 2 of glycogen phosphorylase (PDB code 1abb).
- ↑ These sheets are part of the structure of human transferrin n-lobe mutant (PDB code 1dtg).