Is E37, a major polypeptide of the inner membrane from plastid envelope, an S-adenosyl methionine-dependent methyltransferase?
Using antibodies raised against E37, one of the major polypeptides of the inner membrane from the chloroplast envelope, it has been demonstrated that a single immunologically related polypeptide was present in total protein extracts from various higher plants (monocots and dicots), in photosynthetic and non-photosynthetic tissues from young spinach plantlets, as well as in the cytoplasmic membrane from the cyanobacteria Synechococcus. This ubiquitous distribution of E37 strongly suggests that this protein plays an envelope-specific function common to all types of plastids. Comparison of tobacco and spinach E37 amino acid sequences deduced from the corresponding cDNA demonstrates that consensus motifs for S-adenosyl methionine-dependent methyltransferases are located in both sequences. This hypothesis was confirmed using a biochemical approach. It was demonstrated that E37, together with two minor spinach chloroplast envelope polypeptides of 32 and 39 kDa, can be specifically photolabeled with [3H]-S-adenosyl methionine upon UV-irradiation. Identification of E37 as a photolabeled polypeptide was established by immunoprecipitation. Furthermore, photolabeling of the three envelope polypeptides was specifically inhibited by very low concentration of S-adenosyl homocysteine, thus providing evidence for the presence within these proteins of S-adenosyl methionine- and S-adenosyl homocysteine-binding sites that were closely associated. Taken as a whole these results strongly suggest that E37 is an ubiquitous plastid envelope protein that probably has an S-adenosyl methionine-dependent methyltransferase activity. The 32 and 39 kDa envelope polypeptides probably have a similar methyltransferase activity.
Teyssier
E
E
Laboratoire de Physiologie Cellulaire Végétale (URA CNRS no. 576), DBMS, CEA-Grenoble et Université, France.
Block
M A
MA
Douce
R
R
Joyard
J
J
D000595:Amino Acid Sequence; D015153:Blotting, Western; D060365:Chloroplast Proteins; D008780:Methyltransferases / Q000737:chemistry*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry*; D018087:Plastids / Q000737:chemistry*; D016415:Sequence Alignment
D060365:Chloroplast Proteins; D010940:Plant Proteins; D008780:Methyltransferases; C093871:methionine S-methyltransferase