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A comparison of techniques for isolation of the outer membrane proteins of Haemophilus influenzae type b
Abstract:
We compared several rapid techniques used for extraction of outer membrane proteins from gram-negative enteric bacteria to Haemophilus influenzae type b. After lysis of cells with a French press, the inner and outer membranes were separated by isopycnic centrifugation. Each membrane was identified by density, morphology, enzymatic activity, and susceptibility to solid-phase iodination of intact cells. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we identified 10 polypeptides which were enriched in the outer membrane band compared to the inner membrane band. Using these proteins, we compared the polypeptide pattern of outer membranes with that obtained by (1) selective solubilization with sodium dodecyl-beta-D-maltoside, octyl-beta-D-glucopyranoside, Triton X-100, sodium, or cholamidopropyl dimethylaminopropanesulfonate; (2) extraction with chaotropic agents and heat; and (3) differential centrifugation of vesicles shed during transition from log growth phase to stationary growth phase. There were definable differences between the polypeptide pattern of membranes obtained with each rapid technique compared to the polypeptide pattern of isolated outer membranes. The polypeptide pattern of lithium extracts and the Triton X-100 insoluble fractions of total membranes most closely approximated the polypeptide pattern of isopycnically isolated outer membranes. Depending on the outer membrane protein sought, one of these rapid techniques can be utilized when a rapid method of outer membrane protein isolation is required.
Insights
Researchers compared rapid methods for isolating outer membrane proteins from gram-negative bacteria. Lithium extracts and Triton X-100 insoluble fractions most closely matched isolated outer membranes, offering viable rapid isolation techniques.
Area of Science:
- Microbiology
- Protein Biochemistry
Background:
- Outer membrane proteins (OMPs) are crucial for gram-negative bacteria.
- Efficient isolation of OMPs is vital for research and diagnostics.
- Existing methods can be time-consuming.
Purpose of the Study:
- To compare the efficacy of various rapid techniques for isolating outer membrane proteins.
- To identify which rapid methods best replicate the OMP profile of isopycnically purified membranes.
Main Methods:
- Gram-negative bacteria (Haemophilus influenzae type b) were lysed using a French press.
- Inner and outer membranes were separated via isopycnic centrifugation.
- OMP profiles were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
- Rapid isolation techniques included selective solubilization, chaotropic agent extraction, and differential centrifugation.
Main Results:
- SDS-PAGE identified 10 polypeptides enriched in the outer membrane fraction.
- Significant differences were observed between rapid techniques and isopycnic isolation.
- Lithium extracts and Triton X-100 insoluble fractions showed the closest polypeptide patterns to isolated outer membranes.
Conclusions:
- Rapid isolation techniques for outer membrane proteins vary in their effectiveness.
- Lithium extraction and Triton X-100 insoluble fractions are promising rapid methods for OMP isolation.
- The choice of rapid technique depends on the specific outer membrane protein of interest.