The glucan synthase complex of the human pathogenic mold Aspergillus fumiga
tus has been investigated. The genes encoding the putative catalytic subuni
t Fks1p and four Rho proteins of A. fumigatus were cloned and sequenced. Se
quence analysis showed that AfFks1p was a transmembrane protein very simila
r to other Fksp proteins in yeasts and in Aspergillus nidulans. Heterologou
s expression of the conserved internal hydrophilic domain of AfFks1p aas ac
hieved in Escherichia coli. Anti-Fks1p antibodies labeled the apex of the g
erm tube, as did aniline blue fluorochrome, which was specific for beta (1-
3) glucans, showing that AfFks1p colocalized with the newly synthesized bet
a (1-3) glucans. AfRHO1, the most homologous gene to RHO1 of Saccharomyces
cerevisiae, was studied for the first time in a filamentous fungus. AfRho p
roteins have GTP binding and hydrolysis consensus sequences identical to th
ose of yeast Rho proteins and have a slightly modified geranylation site in
AfRho1p and AfRho3p. Purification of the glucan synthase complex by produc
t entrapment led to the enrichment of four proteins: Fks1p, Rho1p, a 100-kD
a protein homologous to a membrane Hf-ATPase, and a 160-kDa protein which w
as labeled by an anti-beta (13) glucan antibody and was homologous to ABC b
acterial beta (1-2) glucan transporters.