| Research Abstract |
Titration of the third domain of turkey and chicken ovomucoid (OMTKY3 and OMCHI3, respectively) with U-80,413, a 2-arylpropionic acid derivative, in conjunction with NMR measurements enabled the identification of the amino acids responsible for binding. Molecular modeling of the ligand-protein complexation provided insights into ability of a protein surface to discriminate the U-80,413 enantiomers on the basis of multiple intermolecular interactions. We found that similarities and differences in orientation and intermolecular interactions between the R- and S-enantiomers of U-80,413. The carboxyl groups of each enantiomer engage in electrostatic interactions with positive charge on Arg 21. The carbonyl group on U-80,413's central ring shares a hydrogen bond with NH_3^+ group of Lys 34. The distinguishing difference between enantiomers is the proximity of the phenylgroup of R-enantiomer and Phe 53.
Commercial chicken ovomucoid (OMCHI) and isolated OMCHI by precipitation with organic solvents from egg whites, which are crude, were fractionated by anion- and cation-exchange chromatography. The obtained four fractions were characterized by reversed-phase chromatography, N-terminal sequencing, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, determination of sugar contents and trypsin-inhibitory activities. Three fractions were OMCHI variants differing in carbohydrate composition, especially in sialic acid content, and the other fraction was tentatively termed ovoglycoprotein (OGCHI). These OMCHI variants and OGCHI were bound to aminopropyl-silica gels to evaluate chiral recognition ability. However, neither OMCHI variant gave appreciable chiral recognition ability, while the OGCHI gave much more excellent chiral recognition properties than those of the OMCHI reported previously. This reveals that chiral recognition ability of the OMCHI reported previoulsy comes from the OGCHI,which is present in crude OMCHI as an impurity.
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