Dfi1p Binding to Calmodulin Promotes Filamentation and Cek1p Activation in Candida albicans.
albicans, a dimorphic fungus and human opportunistic pathogen, undergoes hyphal
development in response to many different environmental cues, including growth in
contact with a semi-solid matrix. C. albicans forms hyphae that invade agar when cells
are embedded in or grown on the surface of agar, and the integral membrane protein Dfi1p
is required for this activity. Dfi1p is ... read morerequired for full activation of mitogen
activated protein kinase Cek1p during growth on agar, indicating that Dfi1p is involved
in Cek1p activation under these conditions. The C-terminal tail of Dfi1p has a
calmodulin binding motif, suggesting that Dfi1p binding to calmodulin may affect Cek1p
activation and invasive filamentation. The goal of this work was to determine the
importance of the calmodulin binding motif of Dfi1p in filamentation and signaling. We
show that the C-terminal tail of Dfi1p binds to calmodulin in vitro, and mutations that
affect this region affect both calmodulin binding in vitro and invasive filamentation
when incorporated into the full length Dfi1p protein. Moreover, increasing intracellular
calcium levels leads to calcium-dependent, Dfi1p-dependent Cek1p activation. This
phenomenon may be unique to C. albicans as we did not detect activation of Kss1p in S.
cerevisiae in response to increased intracellular calcium levels, even if Dfi1p is
overexpressed. We propose that conformational changes in Dfi1p in response to
environmental conditions encountered during growth allow the protein to bind calmodulin
and initiate a signaling cascade that activates
Thesis (Ph.D.)--Tufts University, 2013.
Submitted to the Dept. of Molecular Microbiology.
Advisor: Carol Kumamoto.
Committee: Ralph Isberg, Ekaterina Heldwein, and Abraham Sonenshein.
Keyword: Microbiology.read less