The Search for Cryptic L-Rhamnosyltransferases on the Genome.

The fungal cell wall is an attractive structure to look for new antifungal drug targets and for understanding the host-fungus interaction. is one of the main causative agents of both human and animal sporotrichosis and currently is the species most studied of the genus. The cell wall of this organism has been previously analyzed, and rhamnoconjugates are signature molecules found on the surface of both mycelia and yeast-like cells. Similar to other reactions where sugars are covalently linked to other sugars, lipids, or proteins, the rhamnosylation process in this organism is expected to involve glycosyltransferases with the ability to transfer rhamnose from a sugar donor to the acceptor molecule, i.e., rhamnosyltransferases. However, no obvious rhamnosyltransferase has thus far been identified within the proteome or genome. Here, using a Hidden Markov Model profile strategy, we found within the genome five putative genes encoding for rhamnosyltransferases. Expression analyses indicated that only two of them, named and , were significantly expressed in yeast-like cells and during interaction with the host. These two genes were heterologously expressed in , and the purified recombinant proteins showed rhamnosyltransferase activity, dependent on the presence of UDP-rhamnose as a sugar donor. To the best of our knowledge, this is the first report about rhamnosyltransferases in .