Variability of low-molecular-weight, heat-modifiable outer membrane proteins of Neisseria meningitidis.

Analysis of major outer membrane protein (MOMP) profiles of various meningococci by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (SDS-PAGE) revealed the presence of 0 to 2 low-molecular-weight, heat-modifiable MOMPs (molecular weight, 25,000 to 32,000) and 1 to 3 high-molecular-weight MOMPs (molecular weight, 32,000 to 46,000). Heat modifiability was investigated by comparing MOMP profiles after heating in SDS solutions at 100 degrees C for 5 min or at 40 degrees C for 1 h. Low-molecular-weight MOMPs shifted to higher apparent molecular weights after being heated at 100 degrees C. Heat modifiability of high-molecular-weight MOMPs varied among strains; whenever modified these proteins shifted to lower apparent molecular weights after complete denaturation. Variability of low-molecular-weight, heat-modifiable MOMPs was demonstrated when MOMP profiles were compared of (i) isolates from index cases and associated cases and carriers among contacts, (ii) different isolates from the same individual, and (iii) isolates from a small epidemic caused by serogroup W-135. In some cases high-molecular-weight MOMPs revealed quantitative differences among related strains. The observed variability and quantitative differences indicate that MOMP serotyping and typing on the basis of SDS-PAGE profiles (PAGE typing) need careful reevaluation.