The hemagglutinin (HA) component of the progenitor toxin protects the structural integrity of the neurotoxin; may increase internalization of the neurotoxin into the bloodstream of the host (By similarity). Involved in binding to the small intestine through interactions with glycolipids and glycoproteins containing sialic acid moieties (Probable). The hemagglutinin complex composed of HA-70, HA-33 and HA-17 agglutinates erythrocytes, whereas the individual compenents do not (PubMed:11713244). Erythrocyte agglutination also occurs with the entire toxin complex (PubMed:11713244, PubMed:17581814). Botulinum toxins are produced as large progenitor toxins of 12S (M toxin, about 280 kDa) and 16S (L toxin, about 650 kDa) (PubMed:11713244, PubMed:17581814). M toxin consists of a non-toxic, non-hemagglutinin component (NTNHA) and the neurotoxin (BoNT/D) (PubMed:8569530, PubMed:11713244, PubMed:17581814). L toxin consists of the M toxin and the 3 hemagglutinin (HA) subcomponents of 70, 33, and 17 kDa (PubMed:8569530, PubMed:17581814, PubMed:11713244). The stoichiometry of the whole complex has been modeled as one BoNT/D, one NTNHA, three HA-70, six HA-33 and three HA-17 (PubMed:17581814). HA-33 and HA-17 crystallize as a heterotrimer with two HA-33 and one HA-17 (PubMed:17581814). This protein can also be encoded on a prophage.