Specificity in ligand binding and intracellular signalling by insulin and insulin-like growth factor receptors.
The physiological roles of insulin and insulin-like growth factors (IGFs) are distinct, with insulin acting to regulate cellular uptake and metabolism of fuels, whereas IGFs promote cell growth, survival and differentiation. The only components of signalling pathways known to be unique to insulin and IGFs are their respective receptors, and even these display substantial structural and functional similarity. Specificity of action in vivo must in part reflect relative levels of receptor expression in different tissues. The extent to which the receptors differ in intrinsic signalling capacity remains unclear, but specificity might in principle arise from differences in ligand-binding mechanism or properties of intracellular domains. To identify ligand binding determinants we expressed receptor fragments as soluble proteins. Both N-terminal domains and a C-terminal peptide sequence from the alpha-subunit are essential for ligand binding with moderate affinity. However, binding of ligand with high affinity and specificity requires higher-order structure. To compare signalling capacities, we constructed chimaeras containing intracellular domains of insulin or IGF receptors fused to the extracellular portion of TrkC. Expression and activation of these chimaeras in cell lines reveals subtle differences in signalling and end-point responses, which may depend on cell background.
Siddle
K
K
University of Cambridge, Department of Clinical Biochemistry, Addenbrooke's Hospital, Cambridge CB2 2QR, UK. ks14@mole.bio.cam.ac.uk
Ursø
B
B
Niesler
C A
CA
Cope
D L
DL
Molina
L
L
Surinya
K H
KH
Soos
M A
MA
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D006224:Cricetinae; D007328:Insulin / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D007335:Insulin-Like Growth Factor II / Q000502:physiology*; D008024:Ligands; D008322:Mammals; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D021122:Protein Subunits; D017526:Receptor, IGF Type 1 / Q000737:chemistry / Q000502:physiology*; D017527:Receptor, IGF Type 2 / Q000737:chemistry / Q000502:physiology*; D011972:Receptor, Insulin / Q000737:chemistry / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013379:Substrate Specificity; D014162:Transfection; D018909:src Homology Domains
D007328:Insulin; D008024:Ligands; D021122:Protein Subunits; D017527:Receptor, IGF Type 2; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin