The homodimeric form of glycine N-methyltransferase acts as a polycyclic aromatic hydrocarbon-binding receptor.
In the rat, cytochrome P4501A1 gene expression is thought to be regulated by several trans-acting factors including the 4S polycyclic aromatic hydrocarbon (PAH)-binding protein, which was recently identified as glycine N-methyltransferase [Raha, A., Wagner, C., MacDonald, R. G., and Bresnick, E. (1994) J. Biol. Chem. 268, 5750-5756]. Glycine N-methyltransferase (GNMT) is one of those unique proteins which exhibit diversity in function. Different subunit configurations are involved in its enzymatic role as a methyltransferase and as PAH-binding receptor. Here we report a systematic study of the oligomeric state of GNMT in the presence of benzo[a]pyrene (B[a]P) in vivo and in vitro. We have used chemical cross-linking and denaturing polyacrylamide gel electrophoresis to show that the B[a]P-binding unit of GNMT is a homodimer. We recently reported that phosphorylation is involved in the interaction of B[a]P with the 4S PAH-binding protein [Bhat, R., Weaver, J. A., Wagner, C., Bodwell, J. E., and Bresnick, E. (1996) J. Biol. Chem. 271, 32551-32556]. In the present study, this observation has been amplified by using bacterially expressed GNMT, which was post-translationally modified by a reticulocyte lysate and ATP-generating system. This modification was also accompanied by the formation of homodimers in the presence of B[a]P. These results indicate that post-translational modification is involved in determining the final configuration, i.e., dimeric form, of GNMT which then acts as a PAH-binding receptor.
Bhat
R
R
Department of Pharmacology and Molecular Toxicology, University of Massachusetts Medical Center, Worcester 01655, USA.
Wagner
C
C
Bresnick
E
E
D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism / Q000494:pharmacology; D015153:Blotting, Western; D002458:Cell Fractionation; D002467:Cell Nucleus / Q000737:chemistry / Q000187:drug effects; D003432:Cross-Linking Reagents; D003600:Cytosol / Q000737:chemistry / Q000187:drug effects; D019281:Dimerization; D050938:Glycine N-Methyltransferase; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008297:Male; D008780:Methyltransferases / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018336:Receptors, Aryl Hydrocarbon / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis; D012156:Reticulocytes / Q000737:chemistry
D003432:Cross-Linking Reagents; D018336:Receptors, Aryl Hydrocarbon; D011994:Recombinant Proteins; D001564:Benzo(a)pyrene; D008780:Methyltransferases; D050938:Glycine N-Methyltransferase; C494512:Gnmt protein, rat