The Hemagglutinin-Neuraminidase (HN) from 'La Piedad, Michoacan' porcine rubulavirus (LPMV) interacts specifically with NeuAc alpha 2,3 lactose residues on the target cell. In this work we report the secondary structure of this protein, determined with five different theoretical algorithms. Results indicate that the HN protein is organized in: an intracellular region (from amino acid 1 to 25); in a beta-strand transmembrane region (residue 26 to 47), typically hydrophobic, rigid and solvent inaccessible; and extracellular region (48 to 576), which possesses hemagglutinating and neuraminidase activity. The secondary structure in this region is organized in a beta-loop-beta alternated with few alpha-helices. Regions with structural and functional implications were determined by pattern search and multiple alignment of the HN from LPM with 12 rubulaviruses and paramyxoviruses HN sequences. The low diversity observed among the HN sequences evaluated indicates that in general the structural organization of the protein, and in particular its sugar binding domain, is closely related among both genera, thus suggesting that the sugar binding domain is well preserved through evolution.

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