- carbonyls alternate in direction
- side-chains alternate in direction (pleated, doubling the layers because CA alternates up and down the sheet)
- zig-zag
- phi: -135, psi: +135 (top-left or Rama plot)
- pitch: 7A tall, 2 residues per turn, 3.5A rise between residues
- beta strands together form beta sheets via H-bonding between main-chain backbone carbonyls and amides
- vs. alpha helices, beta-sheets have H-bonds with different segments of peptide, 0.1A H-bond shorter, both are amphipathic
- left-hand twisted in terms of angle between strand crossings
- uninvolved strands on the edges can wrap around and be involved in H-bond with the
other strand to form barrels
- Greek Key Motif (3214 or 4123 topology) (number in the order of translation, ie N-term is 1 and the C-term is the last number)
- anti-parallel - strongest, H-bond perfectly 180 degrees horizontal, dipoles cancel with other strand, more solvent accessible, some bifuricate forming beta-bulge
- parallel - weaker, H-bond in an angle, dipole aligns with other strand, producing a net dipole on one side = unstable, usually burried, less twisted
- mixed - mixture of parallel and anti-parallel strands
Connection Types
- hairpin - When the backbone enters the same end of the sheet that it left.
- right-handed crossover - When the backbone enters the opposite end.
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