title: One-step evolution of a dimer from a monomeric protein.
abstract: Deletion of six amino acids in a surface loop transforms staphylococcal nuclease from a monomeric protein into a very stable dimer (Kd < 1 x 10(-8)M). A 2 A X-ray crystal structure of the dimer (R = 0.176) shows that the carboxy-terminal alpha-helix has been stripped from its normal position in one monomer and is now incorporated into the equivalent position on the adjoining monomer. This swapping creates an association interface of 2900 A 2. A second, smaller interface of 460 A 2 is also formed. The spontaneous exchange or swapping of secondary structural elements provides a simple pathway for the formation of large, stable protein/protein interfaces and may play an important role in the evolution of oligomeric proteins.
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Green
authors.forename: A G
authors.initials: AG
authors.lastname: Gittis
authors.forename: A K
authors.initials: AK
authors.lastname: Meeker
authors.forename: E E
authors.initials: EE
authors.lastname: Lattman
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D005075:Biological Evolution; D002498:Centrifugation; D003851:Deoxyribonucleases / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation; D017384:Sequence Deletion; D013210:Staphylococcus / Q000201:enzymology; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; D003851:Deoxyribonucleases