The hemagglutinating adhesin HA‐Ag2 of Bacteroides gingivalis is distinct from fimbrilin

We carried out a series of immunoblots with antigenic preparations from the periodontal pathogen Bacteroides gingivalis using antisera of restricted specificity for the hemagglutinating adhesin HA‐Ag2, and for the major structural subunit of the fimbriae (fimbrilin). We have been able to show that these 2 antigens are distinct. The fimbrilin subunit had an apparent molecular weight of 42 kDa in all of the bacterial preparations tested. HA‐Ag2 occurred as a pair of bands at 43 and 49 kDa in outer membranes prepared as extracellular vesicles, and at 33 and 38 kDa in glass‐bead‐EDTA extracted antigens and in sheared‐cell outer membranes prepared in the presence of EDTA. No HA‐Ag2 was found in an enriched fimbrial preparation. The 2 antigens could thus be distinguished on the basis of their behaviour when subjected to different extraction techniques. The lower apparent molecular weight of HA‐Ag2 (a pair of bands at 33 and 38 kDa) was invariably associated with the presence of EDTA in the buffers used to prepare the extracts, and the effect could be partially prevented by adding MgCl2 to the extraction buffer. The difference in apparent molecular weight of HA‐Ag2 in the different extracts can thus be attributed either to an EDTA‐sensitive tertiary conformation of its component polypeptides, or to an EDTA‐sensitive linkage of each of these polypeptides to an unknown component of approximately 10 kDa.