The roles of tyrosines 24, 31, and 60 in the high affinity binding of insulin-like growth factor-I to the type 1 insulin-like growth factor receptor.
A series of insulin-like growth factor I (IGF-I) structural analogs in which one or more of the three tyrosine residues were replaced with nonaromatic residues were produced and their binding properties characterized. The single point mutations, [Leu24]IGF-I, [Ala31]IGF-I, and [Leu60]IGF-I result in an 18-, 6-, or 20-fold loss in affinity, respectively, for the type 1 IGF receptor. Multiple mutations, [Ala31,Leu60]IGF-I, [Leu24, Ala31]IGF-I, [Leu24, Leu60]IGF-I, or [Leu24, Ala31, Leu60]IGF-I result in a 520-, 240-, 1200-, or greater than 1200-fold loss in affinity, respectively, at the type 1 IGF receptor. In contrast, none of the analogs display greater than a 2-fold loss in affinity for the acid-stable human serum binding proteins. At the insulin receptor, [Ala31]IGF-I and [Leu24]IGF-I are equipotent to and 5-fold less potent than IGF-I, whereas [Leu60]IGF-I and the multiple mutation analogs are inactive up to 10 microM. Analogs [Leu24]IGF-I, [Ala31]IGF-I, and [Leu24, Ala31]IGF-I are equipotent to IGF-I at the type 2 IGF receptor, whereas all analogs containing Leu60 demonstrate little measurable affinity at this receptor. Thus, Tyr24, Tyr31, and Tyr60 are involved in the high affinity binding of IGF-I to the type 1 IGF receptor, while Tyr60 is important for maintaining binding to the type 2 IGF receptor.
Bayne
M L
ML
Department of Growth Biochemistry, Merck Sharp and Dohme Research Laboratories, Rahway, New Jersey 07065.
Applebaum
J
J
Chicchi
G G
GG
Miller
R E
RE
Cascieri
M A
MA
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D015345:Oligonucleotide Probes; D010957:Plasmids; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*; D014443:Tyrosine
D015345:Oligonucleotide Probes; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D004247:DNA