Identification of the sites of phosphorylation in insulin-like growth factor binding protein-1. Regulation of its affinity by phosphorylation of serine 101.

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Citation

Jones JI, Busby WH Jr, Wright G, Smith CE, Kimack NM, Clemmons DR

Identification of the sites of phosphorylation in insulin-like growth factor binding protein-1. Regulation of its affinity by phosphorylation of serine 101.

J Biol Chem. 1993 Jan 15;268(2):1125-31.

PubMed ID
7678248 [ View in PubMed
]
Abstract

Serine phosphorylation of insulin-like growth factor binding protein-1 (IGFBP-1) has been shown to alter its affinity for the insulin-like growth factors (IGF-I and IGF-II) and to modify its capacity to modulate cellular responses to the IGFs. Because of this, we determined the sites of serine phosphorylation. Purification of 32P-labeled IGFBP-1 was followed by digestion with trypsin and endoproteinase Glu-C and radiosequencing of labeled peptides. Three serines were found to be phosphorylated, with Ser101, Ser119, and Ser169 containing 70%, 5%, and 25% of the incorporated 32P, respectively. A mutated IGFBP-1, substituting alanine for serine at positions 98 and 101, was expressed in CHO cells. On nondenaturing gels, the wild type protein migrated as five isoforms (one non-phosphorylated and four phosphorylated). However, in the mutated protein, the most rapidly migrating band (a phosphorylated form) was not present. The cells containing the mutated cDNA incorporated 60% less 32P into immunoprecipitable IGFBP-1. The mutated protein had a 3-fold reduction in affinity for IGF-I compared to the wild type protein. We conclude that Ser101 represents the major site of phosphorylation containing 63% of the total 32P incorporated and that phosphorylation of Ser101 is important for maintenance of high affinity binding for this growth factor.

DrugBank Data that Cites this Article

Polypeptides
NameUniProt ID
Insulin-like growth factor-binding protein 1P08833Details