Coiled Coils and Leucine Zippers Flashcards
Broadly speaking, how are coiled coils and leucine zipper terms used?
Leu zippers used in context of DNA binding proteins and generally shorter coiled coils.
Coiled coils used more generally and for longer entities.
Why does increasing the number of helices in a coiled coil increase the length of the pitch?
Reflective of an increase in diameter which reflects decreasing amount of space to pack was into hydrophobic core - whole structure must expand to accommodate helices.
What are the preferences for packing for isoleucine and leucine residues?
Isoleucine - prefers parallel packing seen at A sites (beta branched)
Leucine - prefers perpendicular at D sites (gamma branched)
If change Ile from A to D and converse - drive tetramer formation to restore preferred packing geometry.
What did Liu et al show in 2006?
Made a 7 helix coiled coil - based on GCN4
Lysine and glutamate adapt for inter helical salt bridges.
B and Cs quite close - add salt bridges here.
Larger structures - further away Has become more important for packing.
Why are coiled coils useful?
Simplest oligomerisation unit known in biology (30AAs)
Easy to switch between oligomeric STATES, ORIENTATIONS and BINDING PARTNERS by changing a few AAs.
Can change no of heptad repeats and therefore LENGTH.
Can take a number of coiled coils and pack into super coiled coils –> stable proteinaceous structures.
Why do we not see Fos homodimers?
A couple of un-ideal A residues.
5 Glu residues in E and G –> strong repulsion.
How does the fox/Jun heterodimer bind to DNA?
2 alpha helices diverge from DIMER AXIS at junction between basic and zipper regions –> basic regions displaced from dimer interface and can pass through DNA major groove.
Why aren’t coiled coils super stable?
Have to undergo conformational rearrangements.
What two mistakes comprised the driving force for nano cages?
Disulphide bond formation at one end and lysine revulsion at other –> wedge shape arrangement of trimer-dimer interface.
