Small Assemblies
Three to Six Helices
Opening Image: The B domain of Staphylococcus aureus protein A. Packing a pair of α helices at an angle relative to one another permits their contacting side chains to interdigitate efficiently.
surface model.
Small Assemblies
Three to Six Helices
The Oct-1 POU domain from humans, an excellent example of how motifs, in this case the common helix-loop-helix motif are combined to create a fold.
Small Assemblies
Three to Six Helices
Endonuclease III. the assembly of five helices. α-helices tend to pack around a central helix when the assembly contains five or more helices. Note that one helix is broken. The break occurs at a single Gly (green) in the middle of the helix.
Large Assemblies
Farnesyl pyrophosphate synthase. The active enzyme is a homodimer; each subunit is an assembly of 14 helices.
Farnesyl pyrophosphate is an intermediate in the biosynthesis of cholesterol. The mechanism of the synthase-catalyzed reaction is particularly interesting since it is one of the very few known enzyme-catalyzed reactions that proceed via a carbocation intermediate.
spacefilling model. Notice the abundance of positively and negatively charged side chains on the surface. Lys and Arg (shown in blue) versus Asp and Glu (shown in red). Another feature is the deep active site cleft.
Large Assemblies
Glucoamylase: a 13-helix assembly.
spacefilling model. The active site cleft is almost closed.
Assemblies of Long Helices
The N-terminal domain of seryl-tRNA synthetase from Thermus thermophilus: an excellent example of the coiled-coil motif. The curvature of the helices allows intimate packing of the side chains.
transparent view.
Assemblies of Long Helices
Apolipophorin: a protein involved in transport of lipids.
Aspartate receptor from E. coli: a transmembrane signaling protein involved in chemotaxis.
Syntaxin 1A: a part of the apparatus for exocytosis of synaptic vesicles.
spacefilling model of the backbones. What do you observe regarding the number of strong peptide hydrogen bonds? Explain.