Mutagenesis of basic amino acids in the carboxyl-terminal region of insulin-like growth factor binding protein-5 affects acid-labile subunit binding.
Like insulin-like growth factor binding protein-3 (IGFBP-3), IGFBP-5 was recently shown to form ternary complexes with insulin-like growth factor (IGF) and the acid-labile subunit (ALS). Previous studies using IGFBP-5/IGFBP-6 chimeric proteins have identified major and minor ALS binding sites in the carboxyl-terminal and central regions, respectively of IGFBP-5. We now report that ALS binds to IGFBP-3 (K(a) = 1.1 +/- 0.1 liters/nmol) and IGFBP-5 (K(a) = 1.8 +/- 0.5 liters/nmol) with similar binding affinities. Using site-specific mutants, we have identified residues K(211)/R(214)/K(217)/R(218) within the carboxyl-terminal region of IGFBP-5 as being essential for ALS binding. Mutation of K(134)R(136) or K(138)K(139) in the central region of IGFBP-5 resulted in a small decrease in ALS binding.
Firth
S M
SM
Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St. Leonards, New South Wales 2065, Australia. sfrth@med.usyd.edu.au
Clemmons
D R
DR
Baxter
R C
RC
D000595:Amino Acid Sequence; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000737:chemistry / Q000378:metabolism; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship
D018972:Insulin-Like Growth Factor Binding Protein 3; D018975:Insulin-Like Growth Factor Binding Protein 5; D021122:Protein Subunits; D011994:Recombinant Proteins