A novel approach to identify two distinct receptor binding surfaces of insulin-like growth factor II.
Very little is known about the residues important for the interaction of insulin-like growth factor II (IGF-II) with the type 1 IGF receptor (IGF-1R) and the insulin receptor (IR). Insulin, to which IGF-II is homologous, is proposed to cross-link opposite halves of the IR dimer through two receptor binding surfaces, site 1 and site 2. In the present study we have analyzed the contribution of IGF-II residues equivalent to insulin's two binding surfaces toward the interaction of IGF-II with the IGF-1R and IR. Four "site 1" and six "site 2" analogues were produced and analyzed in terms of IGF-1R and IR binding and activation. The results show that Val(43), Phe(28), and Val(14) (equivalent to site 1) are critical to IGF-1R and IR binding, whereas mutation to alanine of Gln(18) affects only IGF-1R and not IR binding. Alanine substitutions at Glu(12), Asp(15), Phe(19), Leu(53), and Glu(57) analogues resulted in significant (>2-fold) decreases in affinity for both the IGF-1R and IR. Furthermore, taking a novel approach using a monomeric, single-chain minimized IGF-1R we have defined a distinct second binding surface formed by Glu(12), Phe(19), Leu(53), and Glu(57) that potentially engages the IGF-1R at one or more of the FnIII domains.
Alvino
Clair L
CL
School of Molecular and Biomedical Science, The University of Adelaide, Gate 8, Victoria Drive, Adelaide, South Australia 5005, Australia.
McNeil
Kerrie A
KA
Ong
Shee Chee
SC
Delaine
Carlie
C
Booker
Grant W
GW
Wallace
John C
JC
Whittaker
Jonathan
J
Forbes
Briony E
BE
D019943:Amino Acid Substitution; D000818:Animals; D041702:BALB 3T3 Cells; D001665:Binding Sites / Q000502:physiology; D019281:Dimerization; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D020125:Mutation, Missense; D010449:Peptide Mapping / Q000379:methods; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D017526:Receptor, IGF Type 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011972:Receptor, Insulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin