Immunoglobulin can be functionally regulated by protein carboxylmethylation in Fc region.
Protein carboxylmethylation methylates the free carboxyl groups in various substrate proteins by protein carboxyl O-methyltransferase (PCMT) and is one of the post-translational modifications. There have been many studies on protein carboxylmethylation. However, the precise functional role in mammalian systems is unclear. In this study, immunoglobulin, a specific form of gamma-globulin, which is a well-known substrate for PCMT, was chosen to investigate the regulatory roles of protein carboxylmethylation in the immune system. It was found that the anti-BSA antibody could be carboxylmethylated via spleen PCMT to a level similar to gamma-globulin. This carboxylmethylation increased the hydrophobicity of the anti-BSA antibody up to 11.4%, and enhanced the antigen-binding activity of this antibody up to 24.6%. In particular, the Fc region showed a higher methyl accepting capacity with 80% of the whole structure level. According to the amino acid sequence alignment, indeed, 7 aspartic acids and 5 glutamic acids, as potential carboxylmethylation sites, were found to be conserved in the Fc portion in the human, mouse and rabbit. The carboxylmethylation of the anti-BSA antibody was reversibly demethylated under a higher pH and long incubation time. Therefore, these results suggest that protein carboxylmethylation may reversibly regulate the antibody-mediated immunological events via the Fc region.
Park
Jong Sun
JS
Department of Genetic Engineering, Faculty of Life Science and Technology, Sungkyunkwan University, Suwon 440-746, Korea.
Cho
Jae Youl
JY
Kim
Sung Soo
SS
Bae
Hyun Jin
HJ
Han
Jeung Whan
JW
Lee
Hyang Woo
HW
Hong
Sung Youl
SY
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000737:chemistry / Q000276:immunology* / Q000302:isolation & purification; D001666:Binding Sites, Antibody / Q000276:immunology; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry / Q000276:immunology; D007141:Immunoglobulin Fc Fragments / Q000737:chemistry / Q000276:immunology*; D007074:Immunoglobulin G / Q000737:chemistry / Q000276:immunology*; D008745:Methylation; D008969:Molecular Sequence Data; D010206:Papain; D011497:Protein O-Methyltransferase / Q000737:chemistry / Q000378:metabolism*; D011817:Rabbits; D016415:Sequence Alignment; D012710:Serum Albumin, Bovine / Q000276:immunology
D000906:Antibodies; D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D012710:Serum Albumin, Bovine; D011497:Protein O-Methyltransferase; D010206:Papain