Structure-function relationships of S-carboxymethyl methionine27 glucagon.
Carboxymethylation of glucagon and subsequent purification of the hormone has provided a derivative modified by the addition of bulk to the methionine at position 27 without a net charge alteration in the side chain. Unreacted glucagon was removed after methylation of the methionine which provides a positively charged chromatographic handle. The derivative has a half-maximum concentration for binding of 5.3 nM and is a full agonist. These findings along with those provided by methylation of the methionine indicate that a positive charge rather than bulk on the methionine side chain disrupts the binding of hormone to its receptor. The S-carboxymethyl derivative lacks the concentration-dependent aggregation characteristic of glucagon at pH 10.2 as does the S-methyl derivative but increases its helical content in 30% 2-chloroethanol to the same extent as native and S-methyl hormone. Full activity of the S-carboxymethyl methionine27 glucagon does not favor the existence of the globular structure proposed by Korn and Ottensmeyer [(1983) J. Theor. Biol. 105, 403] as the binding species whereas multiple considerations do favor a flexible hormone with nucleation followed by conformational changes for complete binding and activation. Isotopic enrichment using labeled iodoacetate is feasible and can provide more definitive structural information.
Cornely
K A
KA
Shelter
K A
KA
England
R D
RD
Horwitz
E M
EM
Gurd
R S
RS
D000262:Adenylyl Cyclases / Q000378:metabolism; D001667:Binding, Competitive; D001681:Biological Assay; D002942:Circular Dichroism; D004789:Enzyme Activation; D005934:Glucagon / Q000031:analogs & derivatives*; D007700:Kinetics; D011487:Protein Conformation; D011956:Receptors, Cell Surface / Q000378:metabolism; D018027:Receptors, Glucagon; D013329:Structure-Activity Relationship
D011956:Receptors, Cell Surface; D018027:Receptors, Glucagon; D005934:Glucagon; C046110:glucagon, carboxy-Me-Met(27)-; D000262:Adenylyl Cyclases