Abstract:
Cell surface proteins obtained by alkaline extraction from isolated cell
walls of Mortierella pusilla and M. candelabrum, host and nonhost,
respectively, to the mycoparasite, Piptocephalis virginiana, were tested for
their ability to agglutinate mycoparasite spores. The host cell wall protein
extract had a high agglutinating activity (788 a.u. mg- t ) as compared with
the nonhost extract (21 a.li. mg- t ). SDS-polyacrylamide gel electrophoresis
of the cell wall proteins revealed four protein bands, a, b, c, and d (Mr 117,
100, 85 and 64 kd, respectively) at the host surface, but not at the nonhost
surface, except for the faint band c. Deletion of proteins b or c from the
host cell wall protein extract significantly reduced its agglutinating
activity. Proteins band c, obtained as purified preparations by a series of
procedures, were shown to be two glycoproteins. Carbohydrate analysis
by gas chromatography demonstrated that glucose and Nacetylglucosamine
were the major carbohydrate components of the
glycoproteins. It was further shown that the agglutinating activity of the
pure preparation containing both band c was 500-850 times that of the
single glycoproteins, suggesting the involvement of both glycoproteins in
agglutination. The results suggest that the glycoproteins band c are the
two subunits of agglutinin present at the host cell surface.
The two glycoproteins band c purified from the host cell wall protein
extract were further examined after various treatments for their possible
role in agglutination, attachment and appressorium formation by the
mycoparasite. Results obtained by agglutination and attachment tests
showed: (1) the two glycoprotein-s are not only an agglutinin responsible
for the mycoparasite spore agglutination, but may also serve as a receptor for the specific recognition, attachment and appressorium formation by the
mycoparasite; (2) treatment of the rnycoparasite spores with various
sugars revealed that arabinose, glucose and N-acetylglucosamine inhibited
the agglutination and attachment activity of the glycoproteins, however,
the relative percentage of appressorium formation was not affected by the
above sugars; (3) the two glycoproteins are relatively stable with respect
to their agglutinin and receptor functions. The present results suggest that
the agglutination and attachment may be mediated directly by certain
sugars present at the host and mycoparasite cell surfaces while the
appressorlum formation may be the response of complementary
combinations of both sugar and protein, the two parts of the glycoproteins
at the interacting surfaces of two fungi.
