The center of a protein
that consists of the hydrophobic
groups (naturally) packed
into an almost crystal
line state. Since this is the framework of the structure it is most often conserved
. In other words, proteins might vary on their surface
s - where this will not affect the shape - but not inside.
Similar folds may therefore have similar core packing, although it is a sort of knapsack problem. Combinatorial arrangements of sidechains allow several different possible tilings (as it were). However, for a given set of residues there will be a few arrangements that fold swiftly and stably.