Mutation of interfaces in domain-swapped human betaB2-crystallin.
The superfamily of eye lens betagamma-crystallins is highly modularized, with Greek key motifs being used to form symmetric domains. Sequences of monomeric gamma-crystallins and oligomeric beta-crystallins fold into two domains that pair about a further conserved symmetric interface. Conservation of this assembly interface by domain swapping is the device adopted by family member betaB2-crystallin to form a solution dimer. However, the betaB1-crystallin solution dimer is formed from an interface used by the domain-swapped dimer to form a tetramer in the crystal lattice. Comparison of these two structures indicated an intriguing relationship between linker conformation, interface ion pair networks, and higher assembly. Here the X-ray structure of recombinant human betaB2-crystallin showed that domain swapping was determined by the sequence and not assembly conditions. The solution characteristics of mutants that were designed to alter an ion pair network at a higher assembly interface and a mutant that changed a proline showed they remained dimeric. X-ray crystallography showed that the dimeric mutants did not reverse domain swapping. Thus, the sequence of betaB2-crystallin appears well optimized for domain swapping. However, a charge-reversal mutation to the conserved domain-pairing interface showed drastic changes to solution behavior. It appears that the higher assembly of the betagamma-crystallin domains has exploited symmetry to create diversity while avoiding aggregation. These are desirable attributes for proteins that have to exist at very high concentration for a very long time.
Smith
Myron A
MA
Department of Crystallography, Institute of Structural and Molecular Biology, Birkbeck College, University of London, London WC1E 7HX, United Kingdom.
Bateman
Orval A
OA
Jaenicke
Rainer
R
Slingsby
Christine
C
D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D002942:Circular Dichroism; D003459:Crystallins / Q000737:chemistry* / Q000235:genetics; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D017386:Sequence Homology, Amino Acid
D003459:Crystallins