TAILIEUCHUNG - Báo cáo Y học: The opgGIH and opgC genes of Rhodobacter sphaeroides form an operon that controls backbone synthesis and succinylation of osmoregulated periplasmic glucans

Osmoregulated periplasmic glucans (OPGs) ofRhodobacter sphaeroidesare anionic cyclic molecules that accumulate in large amounts in the periplasmic space in response to low osmolarity of the medium. Their anionic character is pro-vided by the substitution of the glucosidic backbone by succinyl residues. A wild-type strain was subject to trans-poson mutagenesis, and putative mutant clones were screened for changes in OPGs by thin layer chromatogra-phy. | Eur. J. Biochem. 269 2473-2484 2002 FEBS 2002 doi The opgGIH and opgC genes of Rhodobacter sphaeroides form an operon that controls backbone synthesis and succinylation of osmoregulated periplasmic glucans Virginie Cogez1 Evgueni Gak2 Agnes Puskas2 Samuel Kaplan2 and Jean-Pierre Bohin1 1Unite de Glycobiologie Structurale et Fonctionnelle CNRS UMR8576 Universite des Sciences et Technologies de Lille France department of Microbiology and Molecular Genetics University of Texas Health Scienee eenter Houston TX C .Al Osmoregulated periplasmic glucans OPGs of RhodobacSée sphaeroides are anionic cyclic molecules that accumulate in large amounts in the periplasmic space in response to low osmolarity of the medium. Their anionic character is provided by the substitution of the glucosidic backbone by succinyl residues. A wild-type strain was subject to transposon mutagenesis and putative mutant clones were screened for changes in OPGs by thin layer chromatography. One mutant deficient in succinyl substitution of the OPGs was obtained and the gene inactivated in this mutant was characterized and named opgC. opgC is located downstream of three ORFs opgGIH two of which are similar to the Escherichia coli operon mdoGH governing OPG backbone synthesis. Inactivation of opgG opgl or opgH abolished OPG production and complementation analysis indicated that the three genes are necessary for backbone synthesis. In contrast inactivation of a gene similar to ndvB encoding the OPG-glucosyl transferase in Sinorhizobium meliloti had no consequence on OPG synthesis in Rhodobacter sphaeroides. Cassette insertions in opgH had a polar effect on glucan substitution indicating that opgC is in the same transcription unit. Expression of opglHC in E. coli mdoB mdoC and mdoH mutants allowed the production of slightly anionic and abnormally long linear glucans. Keywords periplasm osmoregulation cyclic glucans glucosyl transferase operon. Osmoregulated periplasmic .

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