Figure 4
The size of crystal-packing interfaces. Distribution of the interface area B of 1320 pairs of molecules in crystals of monomeric proteins analyzed by Janin & Rodier (1995 ). The average is B = 570 Å2. Interfaces with values of B comparable to those found in protein–protein complexes (B > 800 Å2) occur mostly in crystals with twofold symmetry; they form `crystal dimers' that may be mistaken for real homodimers. In crystals with no twofold symmetry, the number of packing interfaces with B > 800 Å2 follows an extreme value distribution, approximated here by the red line (Janin, 1997 ). The boxed region includes 103 crystal dimers and 85 other large crystal-packing interfaces whose properties may be compared with those of the interfaces in complexes and homodimers (Bahadur et al., 2004 ). |