title: Dimer-tetramer transition between solution and crystalline states of streptavidin and avidin mutants.
abstract: The biotin-binding tetrameric proteins, streptavidin from Streptomyces avidinii and chicken egg white avidin, are excellent models for the study of subunit-subunit interactions of a multimeric protein. Efforts are thus being made to prepare mutated forms of streptavidin and avidin, which would form monomers or dimers, in order to examine their effect on quaternary structure and assembly. In the present communication, we compared the crystal structures of binding site W-->K mutations in streptavidin and avidin. In solution, both mutant proteins are known to form dimers, but upon crystallization, both formed tetramers with the same parameters as the native proteins. All of the intersubunit bonds were conserved, except for the hydrophobic interaction between biotin and the tryptophan that was replaced by lysine. In the crystal structure, the binding site of the mutated apo-avidin contains 3 molecules of structured water instead of the 5 contained in the native protein. The lysine side chain extends in a direction opposite that of the native tryptophan, the void being partially filled by an adjacent lysine residue. Nevertheless, the binding-site conformation observed for the mutant tetramer is an artificial consequence of crystal packing that would not be maintained in the solution-phase dimer. It appears that the dimer-tetramer transition may be concentration dependent, and the interaction among subunits obeys the law of mass action.
authors.affiliation: Department of Biological Chemistry, The Institute of Life Sciences, The Wolfson Centre for Applied Structural Biology, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel.
authors.forename: Yael
authors.initials: Y
authors.lastname: Pazy
authors.forename: Yael
authors.initials: Y
authors.lastname: Eisenberg-Domovich
authors.forename: Olli H
authors.initials: OH
authors.lastname: Laitinen
authors.forename: Markku S
authors.initials: MS
authors.lastname: Kulomaa
authors.forename: Edward A
authors.initials: EA
authors.lastname: Bayer
authors.forename: Meir
authors.initials: M
authors.lastname: Wilchek
authors.forename: Oded
authors.initials: O
authors.lastname: Livnah
mesh_terms: D000818:Animals; D001360:Avidin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D001710:Biotin / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002645:Chickens / Q000378:metabolism; D003460:Crystallization; D018360:Crystallography, X-Ray; D019281:Dimerization; D004529:Egg White; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D012996:Solutions; D019809:Streptavidin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013302:Streptomyces / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D012996:Solutions; C017071:biotin-binding proteins; D001360:Avidin; D001710:Biotin; D019809:Streptavidin