Alpha Beta Structures

TIM barrel or α/β barrel

β-α-β right handed motifs.

from triosephosphate isomerase.

8 parallel strands and helices. strand 1 and 8 are bonded. structural stability.

loop regions at C end of the strands are for catalytic chemistry / active sites.

β sheet and α helices have hydrophobic side chains packed together. VIL preferred branched hydrophobic.

Other side of β sheet is hydrophobic barrel core. bulky hydrophobic residues take up space. this is so catalysis takes place without solvent / water interfering.

pyruvate kinase is formed by a α/β barrel in the middle, 2 beta sheets above, and twisted sheet below.

horseshoe fold

Leucine repeats 2,5,7,12,20,24. β strand - loop - α helix

e.g. 17-strand + 16-helix ribonuclease inhibitor.

Open curved beta sheet like a horseshoe, not closed like a barrel.

Hydrophobic core, but solvent exposed on inner beta sheet.

open twisted α/β

beta sheet with alpha helices on both sides.

active site is at the top of the sheet.

Active site is in crevice when the loops are on opposite sides.

Crevice is different to funnel in a barrel.

hydrophobic between α-β-α