Preparation and characterisation of envelope proteins from Haemophilus pleuropneumoniae

Envelope proteins of Haemophilus pleuropneumoniae were extracted by 3 methods and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Three major envelope proteins (45,000 Mr, 41,000 Mr, 31,500 Mr) were distinguished in sonicated cell envelopes together with minor proteins. Using selective solubilisation with sodium lauryl sarcosinate or Triton X-100, outer membrane proteins were distinguished from those of the cytoplasmic membrane. Extraction into LiCl produced a similar profile, but the 41,000 Mr and 31,500 Mr bands were present in reduced amounts. Extraction into saline at 60 degrees C produced a grossly different pattern, with a major band at 20,000 Mr. All 3 major envelope proteins were shown to be heat-modifiable, and the 31,500 Mr band was found to be the non-heat-modified form of a 43,000 Mr protein, which showed similar properties to the Protein d of H. influenzae which is related to the OmpA protein of E. coli K-12. The 45,000 Mr major protein was also weakly associated with the peptidoglycan in SDS/Triton at low temperature.