The Orientation of Nisin in Membranes

Nisin is a 34 residue long peptide belonging to the group A lantibiotics with antimicrobial activity against Gram-positive bacteria. The antimicrobial activity is based on pore formation in the cytoplasmic membrane of target organisms. The mechanism which leads to pore formation remains to be clarified. We studied the orientation of nisin via site-directed tryptophan fluorescence spectroscopy. Therefore, we engineered three nisin Z variants with unique tryptophan residues at positions 1, 17, and 32, respectively. The activity of the tryptophan mutants against Gram-positive bacteria and in model membrane systems composed of DOPC or DOPG was established to be similar to that of wild type nisin Z. The tryptophan fluorescence emission maximum showed an increasing blue-shift upon interaction with vesicles containing increased amounts of DOPG, with the largest effect for the 1W peptide. Studies with the aqueous quencher acrylamide showed that all tryptophans became inaccessible from the aqueous phase in the presence of negatively charged lipids in the vesicles. From these results it is concluded that anionic lipids mediate insertion of the tryptophan residues in at least three positions of the molecule into the lipid bilayer. The depth of insertion of the tryptophan residues was determined via quenching of the tryptophan fluorescence by spin-labeled lipids. The results showed that the depth of insertion was dependent on the amount of negatively charged lipids. In membranes containing 50% DOPG, the distances from the bilayer center were determined to be 15.7, 15.0, and 18.4 Å for the tryptophan at position 1, 17, and 32, respectively. In membranes containing 90% DOPG, these distances were calculated to be 10.8, 11.5, and 13.1 Å, respectively. These results suggest an overall parallel average orientation of nisin in the membrane, with respect to the membrane surface, with the N-terminus more deeply inserted than the C-terminus. These data were used to model the orientation of nisin in the membrane

Quality of life after surgery for colon cancer in patients with Lynch syndrome: partial versus subtotal colectomy.

Contains fulltext : 109239.pdf (publisher's version ) (Open Access)BACKGROUND: Lynch syndrome is a disorder caused by mismatch repair gene mutations. Mutation carriers have a high risk of developing colorectal cancer. In patients with Lynch syndrome in whom colon cancer has been diagnosed, in general, subtotal colectomy instead of partial colectomy is recommended because of the substantial risk of metachronous colorectal cancer. However, the effect of more extensive surgery on quality of life and functional outcome is unknown. OBJECTIVE: The aim of this study was to investigate quality of life and functional outcome in patients with Lynch syndrome after partial colectomy and subtotal colectomy. DESIGN: This is a nationwide cross-sectional study in the Netherlands. SETTINGS: Two quality-of-life questionnaires (Short Form-36 and The European Organization for Research and Treatment of Cancer Colorectal Cancer-specific Quality of Life Questionnaire Module) and a functional outcome questionnaire (Colorectal Functional Outcome) were used. PATIENTS: Patients with Lynch syndrome who underwent surgery for colon cancer were included. MAIN OUTCOME MEASURES: The primary outcomes measured were quality of life and functional outcome. RESULTS: Questionnaires were sent to 192 patients with Lynch syndrome who underwent surgery for colorectal cancer. A total of 136 patients returned the questionnaire (response rate, 71%). Eighteen patients with rectal cancer, 9 patients with a permanent ileostomy, and 5 patients with an IPAA were excluded. Fifty-one patients underwent partial colectomy, and 53 underwent subtotal colectomy. None of the scales of the Short Form-36 survey showed a significant difference. Analysis of the Colorectal Functional Outcome questionnaire revealed that, after subtotal colectomy, patients have a significantly higher stool frequency (p </= 0.01) and a significantly higher score on stool-related aspects (p = 0.06) and social impact (p = 0.03). The European Organization for Research and Treatment of Cancer Colorectal Cancer-specific Quality of Life Questionnaire Module presented more problems with defecation after subtotal colectomy (p </= 0.01). LIMITATIONS: Certain selection bias cannot be ruled out. CONCLUSIONS: Although functional outcome is worse after subtotal colectomy than after partial colectomy, generic quality of life does not differ after the 2 types of surgery in Lynch syndrome. When discussing the options for surgery with the patient, all advantages and disadvantages of both surgical procedures, including quality of life and functional outcome, should be discussed.01 juni 201

Components required for membrane assembly of newly synthesized K+ channel KcsA

An Escherichia coli in vitro transcription-translation system was used to study the components involved in the biogenesis of the homotetrameric potassium channel KcsA. We show that a functional signal recognition particle pathway is essential for tetramer formation, probably to direct correct monomer insertion in the membrane. In the absence of YidC or at reduced SecYEG levels, KcsA assembly occurs with lower efficiency. Strikingly, the highest efficiency of tetramerization was observed when transcription-translation was carried out in the presence of pure lipid vesicles, demonstrating that a phospholipid bilayer is the minimal membrane requirement to form the KcsA tetramer. It is concluded that SecYEG and YidC are not required for the formation of tetrameric KcsA in vitro.