A very tight turn linking adjacent strands of an antiparallel beta-sheet is a beta turn, a third type of secondary structure. Nine residues are depicted.
Spacefilling model without side chains. Note the tight packing of the backbone atoms in the turn (residues R1 to R4). It's easy to identify the hydrogen bonds in the beta sheet if we change from structure colors to cpk colors (a carbons are dark gray). Residues R2 and R3 are not involved in the H-bonding pattern of the beta-sheet. The peptide H-bond between R1 and R4 is the last H-bond in the beta-sheet. The tetrapeptide forming this particular beta-turn is Thr-Glu-Gly-Val. This happens to be a Type II beta turn; glycine is generally found in the third position of Type II turns.
It's easy to identify the hydrogen bonds in the beta sheet if we change from structure colors to cpk colors (a carbons are dark gray). Residues R2 and R3 are not involved in the H-bonding pattern of the beta-sheet. The peptide H-bond between R1 and R4 is the last H-bond in the beta-sheet. The tetrapeptide forming this particular beta-turn is Thr-Glu-Gly-Val. This happens to be a Type II beta turn; glycine is generally found in the third position of Type II turns.
The tetrapeptide forming this particular beta-turn is Thr-Glu-Gly-Val. This happens to be a Type II beta turn; glycine is generally found in the third position of Type II turns.