Molecular properties of a hemagglutinin purified from type A Clostridium botulinum

Clostridium botulinum causes the food poisoning disease botulism by producing botulinum neurotoxin, the most potent toxin known. The neurotoxin is produced along with a group of neurotoxin-associated proteins, or NAPs, which protect it from the low pH and proteases of the gastrointestinal tract. Recently, we isolated one of the major components of NAPs, a 33-kDa hemagglutinin (Hn-33) [Fu et al. (1998), J. Protein Chem. 17, 53-60]. In this study, we present molecular properties of Hn-33 derived from several biochemical and biophysical techniques. Hn-33 in pure form requires a 66-fold lower concentration of sugar inhibition of its hemagglutination activity than in its complexed form with the neurotoxin and other NAPs. However, its protease resistance is not affected by sugar binding. Based on FT-IR and circular dichroism (CD) analysis, Hn-33 is a predominantly beta-sheet protein (74-77%). Hn-33 analysis by laser desorption mass spectrometry and size exclusion column chromatography reveals that it exists predominantly in a dimeric form in the aqueous solution. Even a very low concentration of SDS (0.05%) irreversibly destroyed the biological activity of Hn-33 by changing its secondary structure as revealed by far-UV CD analysis.