The isolation and characterisation of a major outer-membrane protein from Bacteroides distasonis.
An outer-membrane protein (OMP) was isolated from a clinical strain of Bacteroides distasonis. Changes in growth media did not appreciably affect the appearance of this protein in crude outer-membrane preparations examined by SDS-PAGE. However, the proportion of the protein relative to other OMPs was greater in 24-h cultures than in 48-h cultures. The protein could not be readily solubilised by various conventional detergent extraction techniques but treatment of the insoluble material at 100 degrees C with SDS released the protein, as did overnight extraction at 37 degrees C with SDS. This OMP was heat-modifiable, and thus was similar to the OmpA protein of Escherichia coli, with a faster mobility on SDS-PAGE when solubilised at 25 degrees C than at 100 degrees C. The critical temperature for conversion was between 80 degrees C and 90 degrees C. Because of the characteristic heat-modifiability, the protein was called B. distasonis HMP-1 (heat modifiable protein-1). Overnight exposure to EDTA or NaCl at 37 degrees C favoured conversion of the 25 degrees C form to the 100 degrees C form. In intact cells, the protein was labelled by a cell-surface radio-iodination procedure, and thus is at least partially exposed at the cell surface. No reactions between the B. distasonis HMP-1 and antibodies to either E. coli OmpA or E. coli porin were found by Western blot analysis. A B. distasonis OM preparation containing predominantly HMP-1 had pore-forming ability in a liposome assay. This study is the first report of the isolation and characterisation of a heat-modifiable OMP in Bacteroides, and it is the first description of pore-forming activity in a Bacteroides OM fraction.
Wexler
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Research Service, VA Wadsworth Medical Center, Los Angeles, CA 90073.
Getty
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Fisher
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D000596:Amino Acids / Q000032:analysis; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification*; D001439:Bacteroides / Q000737:chemistry*; D003429:Cross Reactions; D003470:Culture Media; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D008081:Liposomes; D018272:Porins; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D012995:Solubility
D000596:Amino Acids; D001425:Bacterial Outer Membrane Proteins; D003470:Culture Media; D008081:Liposomes; D018272:Porins; D012967:Sodium Dodecyl Sulfate