HaHyung Kim

CHARACTERIZATION OF MOUSE SWITCH VARIANT ANTIBODIES BY MATRIX-ASSISTED LASER DESORPTION IONIZATION MASS SPECTROMETRY AND ELECTROSPRAY IONIZATION MASS SPECTROMETRY

The amino acid sequences of mouse monoclonal antibodies have been characterized completely by mass spectrometry. Antibodies used in the present study were derived from mouse switch variant cell lines that produce four kinds of immunoglobulin Gs (IgGs). The amino acid sequences of these antibodies had not been estimated from the corresponding DNA sequence, so the sequences of IgGs derived from other strains were used as references in this study. Intra- and interchain disulfide bonds of the IgGs were reduced and carboxymethylated and the products were subjected to proteolytic digestion. The existence of N-linked oligosaccharides also was taken into account. The capabilities and limitations of matrix-assisted laser desorption ionization-time-of-flight mass spectrometry and capillary liquid chromatography-electrospray ionization mass spectrometry are discussed in the structural characterization of the antibodies. Based on our results, allotypes of the antibodies examined are discussed. This study shows that amino acid sequences of proteins, such as IgG, can be investigated without information about the corresponding DNA sequence if appropriate reference sequences derived from other strains can be used.

Post-translational modifications of immunoglobulin G: a mouse IgG variant that lacks the entire CH1 domain.

In the present study, we characterized the post-translational modifications of a short-chain variant of mouse IgG2a that lacks the entire CH 1 domain. The short-chain IgG2a and its proteolytic fragments were subjected to electrospray ionization- and fast atom bombardment-mass spectrometric analyses. It has been demonstrated that approximately 14% of the heavy chain of the short-chain IgG2a is O-glycosylated with a disaccharide of Ga1-GalNAc- at Thr220A in the hinge region. while the Oglycosylation does not occur in its parent IgG2a molecule. Two additional modifications have been detected at the C-termini of both the heavy and light chains of the short-chain IgG2a. Biological significance of the post-translational modifications of the short-chain IgG2a variant is briefly discussed.

Application of 13C NMR spectroscopy to paratope mapping for larger antigen-Fab complexes.

For the purpose of engineering the antibody combining site, mapping residues that are involved in antigen binding provide us with valuable information. By use of13C NMR spectroscopy with selectively13C‐labeled Fv fragments, we have established a general strategy to identify the residues that are perturbed upon binding of small antigen (hapten) molecules [(1990) Biochemistry 30, 6604–6610]. In the present paper, we demonstrate that this strategy can be extended to molecular structural analyses of the complexes of an Fab fragment and a larger antigen molecule such asPseudomonas aeruginosa exotoxin A with a molecular mass of 67 kDa.

13C-NMR spectral analysis of the structures of mouse immunoglobulin G1 carrying allotypes a and j

A novel 13C nuclear magnetic resonance (NMR) method is described for the detection of subtle structural differences between mouse immunoglobulins carrying different allotypes. Fc fragments of mouse IgG1 antibodies carrying allotypes a and j have been selectively labeled with [1-13C]methionine. 13C-NMR spectra have shown that the microenvironment around Met-398 is significantly different for the two kinds of allotypes. Peptide mapping and amino acid sequence analyses have revealed that Val-406 of IgG1 carrying allotype a is substituted for Ile in the case of allotype j. X-ray crystallographic data indicate that Met-398 is in close spatial proximity to Val (Ile)-406. We therefore conclude that the 13C-NMR method can provide us with a novel spectroscopic probe for the structural characterization of allotypic markers.