6 - Tertiary and quaternary protein structure

Helix-loop- helix

2 helices connected by a turn 

Coiled-coil

2 amphipathic a-helices, interact in parallel through their hydrophobic edges  

Helix bundle

several a-helices, associate in antiparallel manner to form a bundle  

Beta-alpha-beta unit

2 parallel B strand linked to an intervening a helix by 2 loops  

Hairpin

2 adjacent antiparallel B strands connected by a B turn   

B meander:

antiparallel sheet composed of sequential B strand connect by loop or turn

Greek key:

4 antiparallel strand 

B sandwich

stacked B strands or sheets  

All a

entirely of a-helices & connecting loops  

All B

ONLY B sheets & connecting loops  

Mixed a/B

contain motifs, a helix and B strand alternate

a + B

local clusters of a helices and B sheet in separate, distinct region 

examples -Helix-loop- helix

CLOCK-BMAL 1 dimer

examples -Helix-turn- helix

Lamba repressor

examples - Coiled-coil

Cortexillin

examples - Helix bundle

Villin / Vinculin 

examples - Beta-alpha-beta unit

Triose phosphate isomerase - a/B barrel  

examples - Hairpin

Antimicrobial protein from Macadamia nut

examples - Greek key

N-terminal domain of Riboflavin synthase