Structural requirements for annexin I-S100C complex-formation.
S100C is a member of the S100 family of EF-hand-type Ca(2+)-binding proteins which are thought to bind to and thereby regulate the activity of cellular target proteins in a Ca(2+)-dependent manner. An intracellular ligand for S100C is the Ca2+/phospholipid-binding protein annexin I and we show here that complex-formation is mediated through unique domains within S100C and annexin I. Using a proteolytically truncated annexin I derivative as well as a number of N-terminal annexin I peptides in liposome co-pelleting and ligand-blotting assays we map the S100C-binding site to the N-terminal 13 residues of annexin I. Similar analyses employing recombinantly expressed S100C mutants reveal that residues D91 to 194 in the unique C-terminal extension of this S100 protein are indispensable for annexin I binding. Interaction between S100C and an N-terminal annexin I peptide containing a tryptoplan at position 11 can also be monitored by fluorescence emission spectroscopy after tryptophan excitation. This analysis indicates that the local environment of the tryptophan in annexin I becomes less aqueous on S100C binding, suggesting a hydrophobic nature of the protein-protein interaction. Thus the structural basis of the annexin 1-S100C complex-formation probably resembles to a large extent that of the well-characterized annexin II-p11 interaction.
Seemann
J
J
Department of Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Federal Republic of Germany.
Weber
K
K
Gerke
V
V
D000818:Animals; D017305:Annexin A1 / Q000378:metabolism*; D001665:Binding Sites; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018076:DNA, Complementary / Q000737:chemistry; D008081:Liposomes / Q000378:metabolism; D008168:Lung / Q000737:chemistry; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D009418:S100 Proteins / Q000235:genetics / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013552:Swine; D014364:Tryptophan / Q000378:metabolism
D017305:Annexin A1; D002135:Calcium-Binding Proteins; D018076:DNA, Complementary; D008081:Liposomes; D009418:S100 Proteins; C072337:S100A11 protein, human; D014364:Tryptophan; D002118:Calcium