title: SAM domains can utilize similar surfaces for the formation of polymers and closed oligomers.
abstract: The mitogen-activated protein kinase (MAPK) Byr2 and its activator Ste4 are involved in the mating pheromone response pathway of Schizosaccharomyces pombe and interact via their SAM domains. SAM domains can self-associate to form higher-order structures, including dimers, polymers and closed oligomers. Ste4-SAM is adjacent to a trimeric leucine zipper domain and we have shown previously that the two domains together (Ste4-LZ-SAM) bind to a monomeric Byr2-SAM with high affinity (Kd approximately 20 nM), forming a 3:1 complex. Here, we map the surfaces of Byr2-SAM and Ste4-SAM that is involved the interaction. A set of 38 mutants of Byr2-SAM and 33 mutants of Ste4-SAM were prepared, covering most of the protein surfaces. These mutants were purified and screened for binding, yielding a map of residues that are required for binding and a complementary map of residues that are not required. We find that the interface maps to regions of the SAM domains that are known to be important for the formation of SAM polymers. These results indicate that SAM domains can create a variety of oligomeric architectures utilizing common binding surfaces.
authors.affiliation: Department of Chemistry and Biochemistry, UCLA-DOE Institute for Genomics and Proteomics, University of California at Los Angeles, Los Angeles, CA 90095-1570, USA.
authors.forename: Ranjini
authors.initials: R
authors.lastname: Ramachander
authors.forename: James U
authors.initials: JU
authors.lastname: Bowie
mesh_terms: D001665:Binding Sites; D019281:Dimerization; D044387:GTP-Binding Protein beta Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics*; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012436:S-Adenosylmethionine / Q000737:chemistry*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000201:enzymology*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020349:Surface Plasmon Resonance
chemical_list: D044387:GTP-Binding Protein beta Subunits; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; C067576:Ste4 protein, S cerevisiae; D012436:S-Adenosylmethionine; C077892:BYR2 protein, S pombe; D020930:MAP Kinase Kinase Kinases