Expression and characterization of the flocculin Flo11/Muc1, a yeast mannoprotein with homotypic properties of adhesion

Department of Biological Sciences, St. John's University, 8000 Utopia Parkway, Queens, NY 11439

^* To whom correspondence should be addressed. Email: drangina{at}stjohns.edu.

	Abstract

The Flo11/Muc1 flocculin has diverse phenotypic effects. Yeast of strain background 1278b require Flo11p to form pseudohyphae, invade agar, adhere to plastic and develop biofilms but they do not flocculate. We show that S. cerevisiae var. diastaticus strains, on the other hand, exhibit Flo11-dependent flocculation and biofilm formation but do not invade agar or form pseudohyphae. In order to study the nature of the Flo11p produced by these two strains we examined secreted Flo11p, encoded by a plasmid-borne gene in which the GPI anchor sequences had been replaced by a histidine tag. A protein of approximately 196 kDa was secreted from both strains which, upon purification and concentration, aggregated into a form of very high molecular mass. When secreted Flo11p was covalently attached to microscopic beads it conferred the ability to specifically bind to S. cerevisiae var. diastaticus cells, which flocculate, but not to 1278b cells, which do not flocculate. This was true for the 196 kD form as well as the high molecular weight form of Flo11p regardless of the strain source. The coated beads bound to diastaticus cells expressing FLO11 and failed to bind to cells with a deletion of FLO11, demonstrating a homotypic adhesive mechanism. Flo11p was shown to be a mannoprotein. Bead to cell adhesion was inhibited by mannose, which also inhibits Flo11-dependent flocculation in vivo, further suggesting that this in vitro system is a useful model for the study of fungal adhesion.