Spectroscopic characterization of the inclusion complex of a luteinizing hormone-releasing hormone agonist, buserelin acetate, with dimethyl-beta-cyclodextrin.
Inclusion complexation of buserelin acetate, and agonist of luteinizing hormone-releasing hormone, with dimethyl-beta-cyclodextrin (DM-beta-CyD) in aqueous solution was studied spectroscopically and its mode of interaction was assessed. Ultraviolet absorption and circular dichroism (CD) spectroscopies indicate that the aromatic side chains of buserelin acetate, L-tryptophan and L-tyrosine residues, are incorporated into the hydrophobic environment of the DM-beta-CyD activity. Furthermore, proton and carbon-13 nuclear magnetic resonance spectroscopies suggest that in addition to the two aromatic side chains, a tertiary butyl D-serine residue is inserted into the DM-beta-CyD cavity from the secondary hydroxyl side. On the other hand, the continuous variation plots for the buserelin acetate: DM-beta-CyD system showed a 1:1 stoichiometry of the complex. Therefore, the complexation should be initiated by the inclusion of one of the three binding sites on the buserelin molecule into DM-beta-CyD, which may in turn prevent the further access of the second cyclodextrin to the other binding sites, probably due to steric hindrance and/or conformational changes of the peptide. These structural features of the complex would account for the stabilizing effect of DM-beta-CyD on the enzymatic degradation of buserelin acetate.
Matsubara
K
K
Pharma Research Laboratories, Hoechst Japan, Ltd., Saitama, Japan.
Irie
T
T
Uekama
K
K
D002064:Buserelin / Q000378:metabolism*; D002942:Circular Dichroism; D003505:Cyclodextrins / Q000378:metabolism*; D006133:Growth Substances / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet; D047392:beta-Cyclodextrins
D003505:Cyclodextrins; D006133:Growth Substances; D047392:beta-Cyclodextrins; C038119:heptakis(2,6-O-dimethyl)beta-cyclodextrin; D002064:Buserelin