Protein-protein interaction at crystal contacts.
Packing contacts are crystal artifacts, yet they make use of the same forces that govern specific recognition in protein-protein complexes and oligomeric proteins. They provide examples of a nonspecific protein-protein interaction which can be compared to biologically relevant ones. We evaluate the number and size of pairwise interfaces in 152 crystal forms where the asymmetric unit contains a monomeric protein. In those crystal forms that have no element of 2-fold symmetry, we find that molecules form 8 to 10 pairwise interfaces. The total area of the surface buried on each molecule is large, up to 4400 A2. Pairwise interfaces bury 200-1200 A2, like interfaces generated at random in a computer simulation, and less than interfaces in protease-inhibitor or antigen-antibody complexes, which bury 1500 A2 or more. Thus, specific contacts occurring in such complexes extend over a larger surface than nonspecific ones. In crystal forms with 2-fold symmetry, pairwise interfaces are fewer and larger on average than in the absence of 2-fold symmetry. Some bury 1500-2500 A2, like interfaces in oligomeric proteins, and create "crystal oligomers" which may have formed in the solution before crystallizing.
Janin
J
J
Laboratoire de Biologie Structurale, CNRS-Université Paris-Sud, Gif-sur-Yvette, France.
Rodier
F
F
D000263:Adenylate Kinase / Q000737:chemistry; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000737:chemistry; D003198:Computer Simulation; D003460:Crystallization; D018360:Crystallography, X-Ray; D016208:Databases, Factual; D010450:Endopeptidases / Q000737:chemistry; D008958:Models, Molecular; D011480:Protease Inhibitors / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry*; D012984:Software
D002135:Calcium-Binding Proteins; D011480:Protease Inhibitors; D011506:Proteins; D000263:Adenylate Kinase; D010450:Endopeptidases