Clostridium botulinum types A, B, C1, and E produce proteins with or without hemagglutinating activity: do they share common amino acid sequences and genes?

Abstract

Clostridium botulinum produce the antigenically distinct 150 kD neurotoxin serotypes (e.g., A, B, C1, and E) and simultaneously proteins, A Hn+, B Hn+, C Hn+, and E Hn-, that have high, low, and no hemagglutinating activity. A Hn+ and B Hn+ are serologically cross-reactive. A Hn+, B Hn+, and C Hn+ found as large aggregates (900-220 kD) can be dissociated on SDS-PAGE into multiple subunits, the smallest for A Hn+, B Hn+ is 17 kD and 27 kD for C Hn+. The 116 kD E Hn- does not aggregate. We determined the sequences of 10-33 amino terminal residues of the 17, 21.5, 35, and 57 kD subunits of A Hn+ and B Hn+. Each of these subunits have unique sequences, indicating that the larger units studies are not homomers or heteromers of smaller units. The subunits of A Hn+ and B Hn+ of comparable size have striking sequence identity (e.g., 21.5 kD subunits from the two are identical and 57 kD subunits have 80% identity). In vitro proteolysis of 116 kD E Hn- with different proteases did not impart hemagglutinating activity to the fragments. The 116 kD E Hn- and one of its proteolytic fragments (87 kD) were partially sequenced. Sixty-two base pairs downstream from the termination codon of the cloned 33 kD subunit of C Hn+, there is an initiation codon followed by an open reading frame for at least 34 amino acid residues (Tsuzuki et al., 1990). The derived amino acid sequence of this open reading frame, we found, has 73-84% sequence identity with those of the 17 kD subunits of A Hn+ and B Hn+ and significant identity with the N-terminal of E Hn-. These highly conserved sequences show existence of genetic linkage among the Hn+ and Hn- proteins.