Figure 7. Sequence relationships for the connecting peptide to transmembrane region of B12 BG genes show two groups, those which have histidine and lysine near the N-terminus of the transmembrane region, and those with a leucine and threonine (arrows).

A helical wheel shows that one side of an alpha helix through transmembrane region is primarily composed of larger residues (F, phenylalanine; I, isoleucine; L, leucine; W, tryptophan) along with a smaller residue (S, serine), while the other side is composed of smaller residues (A, alanine; G glycine; T, threonine; V, valine). This arrangement suggests that one side of the helix forms a flattened surface for interaction as a dimer, with the signature charged residue (K, lysine) near the edge of this interaction zone.