|
(click
on the main point headings to jump to the selected
location in the notes)
Earliest
fungal wall chemistry
1.
Braconnot - 1811
Found
there was always an alkali-resistant
nitrogen-containing residue left after
hot-alkali (1-6N KOH) treatment of
mushrooms.
However,less N than in protein.
Named residue fungin.
2.
Odier - 1825
Discovered
novel N compound associated with insect
exoskeleton.
Named it chitin.
Same
compound, but chitin* name stuck.
poly
ß-1->4-N-acetylglucosamine
*Chitin
= tanic
156
(Back
to main points)
Average
chemical composition of fungal vegetative
walls
1.
Polysaccharides ~ 75-85%
microfibrillar (main structural)
nonmicrofibrillar (amorphous
polysaccharides –
less
structural to nonstructural).
2.
Protein ~ 10-15% (both structural*
and enzymatic)
3.
Lipid ~ 5-10% (structural)
Also
1)
pigments (usually small amounts,
sometimes high)
2)
phosphate
3)
other inorganic ions
4)
polymerized organic acids (polyuronides).
*hydrophobins
157
(Back
to main points)
Other
wall polysaccharides
1.
Mannans - as mannoproteins*
2.
S-glucans (soluble** a
&/or
ß glucans)
3.
R-glucans (microfibrillar and
nonmicrofibrillar ß glucans)
4.
Numerous types of
heteropolysaccharides
5.
Various polyuronides (polymers of
glucuronic &/or galacturonic acids)
6.
Variety of aminopolysaccharides other
than chitin or chitosan.
*
Many studies in S.
cerevisiae
**
In strong alkali
160
(Back
to main points)
Why
study fungal chitin?
1.
Chitin is chemically unique and not
found in human cells.
2.
Chitin serves a vital role as a main
structural component of fungal walls.
3.
Chitin synthase substrate analogs
inhibit fungal growth and sometimes lead to
fungal deal
4.
Fungal cell walls serve as main
protective barriers between pathogen and
host, so wall components including chitin
should represent virulence factors
165
(Back
to main points)
"Review"
Polysaccharides
of fungi and fungal-like protoctista
Microfibrillar
polysaccharides
b(1->3)
- (1->6) glucans (most of R glucan)
b(1->4)
glucan = cellulose
b
(1->4) N-acetylglucosamine = chitin
Very
weakly microfibrillar polysaccharide
b(1->4)
glucosamine = chitosan
other wall polysaccharides
also Mannans - as mannoproteins
S-glucans (mostly a,
but some b
glucans)
Heteropolysaccharides
[ mostly soluble in H2O (HOT) and
alkali (COLD), but some resistant (only
soluble in hot alkali)]
Various
polyuronides (polymers of glucuronic and
galacturonic acids)
Various
aminopolysaccharides other than chitin or
chitosan – e.g., galactosamine
polysaccharide
162/163
(Back
to main points)
Mannoproteins
Why
studied?
1.
Main antigenic determinants of
S. cerevisiae and most other fungi
(particularly medically important fungi)
2.
Can be altered by mutagenesis so
structure-function relationships can be
studied.
e.g., How affect mating?
How affect secretion?*
3.
Microbial model for protein
glycosylation via dolichol-p lipid
intermediate
*
many secreted fungal enzymes are
glycosylated.
see
OR 5 for details
175
(Back
to main points)
Fungal
cell wall monosaccharides
Most
fungi
1.
D-glucose
2.
N-acetylglucosamine
3.
D-mannose
Monosaccharides
with taxon association
4.
D-galactose (Ascomycota)
5.
D-galactosamine (
"
)
6.
L-fucose (Mucorales &
Basidiomycota)
7.
D-glucosamine (Mucorales)
8.
D-xylose (Basidiomycota)
9.
Uronic acids (Mucorales)
10.
D-rhamnose (Ascomycota)*
*somewhat
rare
179
(Back
to main points)
Monosaccharide
correlations* for chitin/b-glucan
group
Euascomycotina**
Homobasidiomycotina**
Chytridiomycota
|
|
gal
|
gal-NH2
|
fu
|
Xy
|
|
Euascomycotina
|
+
|
+
|
-
|
-
|
|
Homobasidiomycotina
|
-
|
-
|
+
|
+
|
|
Chytridiomycota
|
-
|
-
|
-
|
-
|
*
Not known if will stand test of time
**
& Fungi Imperfecti counterparts
183
(Back
to main points)
|
