TAILIEUCHUNG - Báo cáo Y học: The plant S-adenosyl-L-methionine:Mg-protoporphyrin IX methyltransferase is located in both envelope and thylakoid chloroplast membranes

Chlorophyll biosynthesis requires a metabolic dialog between the chloroplast envelope and thylakoids where biosynthetic activities are localized. Here, we report the ®rst plant S-adenosyl-L-methionine:Mg-protoporphyrin IX methyltransferase (MgPIXMT) sequence identi®ed in the Arabidopsisgenome owing to its similarity with the Synechocystis sp. | Eur. J. Biochem. 269 240-248 2002 FEBS 2002 The plant 5-adenosyl-L-methionine Mg-protoporphyrin IX methyltransferase is located in both envelope and thylakoid chloroplast membranes Maryse A. Block Arun Kumar Tewari Catherine Albrieux Eric Marechal and Jacques Joyard Laboratoire de Physiologie Cellulaire Végétale CNRSịCEAịUniversité Joseph Fourier DBMS PCV Grenoble France Chlorophyll biosynthesis requires a metabolic dialog between the chloroplast envelope and thylakoids where biosynthetic activities are localized. Here we report the first plant S-adenosyl-L-methionine Mg-protoporphyrin IX methyltransferase MgPjxMT sequence identified in the Arabidopsis genome owing to its similarity with the Synechocystis sp. MgPIXMT gene. After expression in Escherichia coli the recombinant Arabidopsis thaliana cDNA was shown to encode a protein having MgPIXMT activity. The full-length polypeptide exhibits a chloroplast transit peptide that is processed during import into the chloroplast. The mature protein contains two functional regions. The C-terminal part aligns with the Synecho-cystis full-length protein. The corresponding truncated region binds to Ado-met as assayed by UV crosslinking and is shown to harbor the MgPIXMT activity. Down stream of the cleaved transit peptide the 40 N-terminal amino acids of the mature protein are very hydrophobic and enhance the association of the protein with the membrane. In A. thaliana and spinach the MgPIXMT protein has a dual localization in chloroplast envelope membranes as well as in thylakoids. The protein is active in each membrane and has the same apparent size corresponding to the processed mature protein. The protein is very likely a monotopic membrane protein embedded within one leaflet of the membrane as indicated by ionic and alkaline extraction of each membrane. The rationale for a dual localization of the protein in the chloroplast is discussed. Keywords protoporphyrin methyltransferase chloroplast membrane chlorophyll. The .

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