Molecular identification and sequence analysis of Hillarin, a novel protein localized at the axon hillock

The monoclonal antibody Lan3-15 identifies a novel protein, Hillarin, that is localized to the axon hillock of leech neurons. Using this antibody we have identified a full length cDNA coding for leech Hillarin and determined its sequence. The gene encodes a 1274 residue protein with a predicted molecular mass of 144013 Da. Data base searches revealed that leech Hillarin has potential orthologues in fly and nematode and that these proteins share two novel protein domains. The W180 domain is characterized by five conserved tryptophans whereas the H domains share 21 invariant residues. In contrast to the arrangement in fly and nematode the cassette containing the W180 and H domains is repeated twice in leech Hillarin. This suggests that the leech Hillarin sequence originated from a duplication event of an ancestral protein with single cassette structure.