title: Structural basis for the specific interaction of lysine-containing proline-rich peptides with the N-terminal SH3 domain of c-Crk.
abstract: BACKGROUND
  Proline-rich segments in the guanine nucleotide exchange factor C3G bind much more strongly to the N-terminal Src homology 3 domain (SH3-N) of the proto-oncogene product c-Crk than to other SH3 domains. The presence of a lysine instead of an arginine in the peptides derived from C3G appears to be crucial for this specificity towards c-Crk.
  
  
  RESULTS
  In order to understand the chemical basis of this specificity we have determined the crystal structure of Crk SH3-N in complex with a high affinity peptide from C3G (PPPALPPKKR, Kd approximately 2 microM) at 1.5 A resolution. The peptide adopts a polyproline type II helix that binds, as dictated by electrostatic complementarity, in reversed orientation relative to the orientation seen in the earliest structures of SH3-peptide complexes. A lysine in the C3G peptide is tightly coordinated by three acidic residues in the SH3 domain. In contrast, the co-crystal structure of c-Crk SH3-N and a peptide containing an arginine at the equivalent position (determined at 1.9 A resolution) reveals non-optimal geometry for the arginine and increased disorder.
  
  
  CONCLUSIONS
  The c-Crk SH3 domain engages in an unusual lysine-specific interaction that is rarely seen in protein structures, and which appears to be a key determinant of its unique ability to bind the C3G peptides with high affinity.
authors.affiliation: Rockefeller University, New York, NY 10021, USA.
authors.forename: X
authors.initials: X
authors.lastname: Wu
authors.forename: B
authors.initials: B
authors.lastname: Knudsen
authors.forename: S M
authors.initials: SM
authors.lastname: Feller
authors.forename: J
authors.initials: J
authors.lastname: Zheng
authors.forename: A
authors.initials: A
authors.lastname: Sali
authors.forename: D
authors.initials: D
authors.lastname: Cowburn
authors.forename: H
authors.initials: H
authors.lastname: Hanafusa
authors.forename: J
authors.initials: J
authors.lastname: Kuriyan
mesh_terms: D000595:Amino Acid Sequence; D001120:Arginine / Q000378:metabolism; D003196:Computer Graphics; D018360:Crystallography, X-Ray; D020662:Guanine Nucleotide Exchange Factors; D008239:Lysine / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000138:chemical synthesis / Q000378:metabolism*; D011487:Protein Conformation; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D050737:Proto-Oncogene Proteins c-crk; D016415:Sequence Alignment
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D009842:Oligopeptides; D011506:Proteins; D011518:Proto-Oncogene Proteins; D050737:Proto-Oncogene Proteins c-crk; D001120:Arginine; D008239:Lysine