title: The Escherichia coli amidase AmiC is a periplasmic septal ring component exported via the twin-arginine transport pathway.
abstract: The N-acetylmuramoyl-l-alanine amidases of Escherichia coli (AmiA, B and C) are periplasmic enzymes that remove murein cross-links by cleaving the peptide moiety from N-acetylmuramic acid. Ami- cells form chains, indicating that the amidases help to split the septal murein. Interestingly, cells defective in the twin-arginine protein transport (Tat) pathway show a similar division defect. We find that both AmiA and AmiC are routed to the periplasm via Tat, providing an explanation for the Tat- division phenotype. Taking advantage of the ability of Tat to export prefolded (fluorescent) green fluorescent protein (GFP) to the periplasm, we sublocalized AmiA and AmiC in live cells using functional fusions to GFP. Interestingly, the periplasmic localization of the fusions differed markedly. AmiA-GFP appeared to be dispersed throughout the periplasm in all cells. AmiC-GFP similarly appeared throughout the periplasm in small cells, but was concentrated almost exclusively at the septal ring in constricting cells. Recruitment of AmiC to the ring was mediated by an N-terminal non-amidase targeting domain and required the septal ring component FtsN. AmiC therefore replaces FtsN as the latest known recruit to the septal ring and is the first entirely periplasmic component to be localized.
authors.affiliation: Case Western Reserve University, School of Medicine, Department of Molecular Biology and Microbiology, W239, 10900 Euclid Ave., Cleveland, OH 44106, USA.
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Bernhardt
authors.forename: Piet A J
authors.initials: PA
authors.lastname: de Boer
mesh_terms: D000595:Amino Acid Sequence; D002455:Cell Division; D004926:Escherichia coli / Q000201:enzymology* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019897:Periplasm / Q000201:enzymology*; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; C098711:FtsN protein, E coli; D008164:Luminescent Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011993:Recombinant Fusion Proteins; C408585:twin-arginine translocase complex, E coli; D049452:Green Fluorescent Proteins; D009238:N-Acetylmuramoyl-L-alanine Amidase