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. Involved in binding to the small intestine through interactions with glycolipids and glycoproteins containing sialic acid moieties (By similarity). Erythrocyte agglutination only occurs when the entire complex is assembled (PubMed:17581814). Binds eukaryotic host mucins as well as N-acetyl-beta-neuraminic acid, N-acetyl-D-galactosamine and galactose (but not glucose) via 2 sites (By similarity). Botulinum toxins are produced as large progenitor toxins of 12S (M toxin, about 280 kDa) and 16S (L toxin, about 650 kDa). M toxin consists of a non-toxic, non-hemagglutinin component (NTNHA) and the neurotoxin (PubMed:8569530, PubMed:11713244, PubMed:17581814). L toxin consists of the M toxin and the 3 subcomponents of hemagglutinin (HA) (PubMed:8569530, PubMed:11713244, PubMed:9802560, PubMed:17581814). HA is composed of subcomponents of 70, 33, and 17 kDa (PubMed:17581814). 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). Arranged in 2 beta-trefoil domains (called 1 and 2) each with three tandemly repeated subdomains (called alpha, beta and gamma) joined by a short alpha-helix (By similarity). Only subdomains 2-alpha and 2-gamma, in the C-terminal beta-trefoil domain, possess a functional carbohydrate-binding site (By similarity). This protein can also be encoded on a prophage. Extended N-terminus. Extended N-terminus.