Peptidoglycan .Types of Bacterial Cell Walls and their Taxonomic ...

420 SCHLEEFER AND KANDLER BACTERIOL. REV.
TABLE 8. Peptidoglycan types of variations A3,8 and A3-y
Vari- Position 4 Interpeptide bridge Position 3 Species Fig. Refertion
ence
G1y2-3 ' Micrococcus 14f 109
radiodurans
A3# D-Ala - L-Ala3 - I L-Orn B. globosum 22c 145
, L-Ala a L-Thr L-Ala L-Ser - B. longum 22b 200
Gly -- Propionibacte- 15a 345
rtum petersoniu
A3-y D-Ala-- L, L-Dpm S. roseochromo- 15a 19a
genes
G1YS3 Arthrobacter 27a 101
tumescens
peptidoglycan types of this subgroup have been
established. We feel that the differentiation
between subgroup A3 and subgroup A4 is justified
by the different modes of biosynthesis of
their interpeptide bridges. The L-amino acids
and glycine of the interpeptide bridge of subgroup
A3 are activated as their transfer ribonucleic
acid (tRNA) derivatives and added sequentially
to the w-amino group of the Ldiamino
acid (240). In the case of subgroup A4,
however, the dicarboxylic amino acids are always
linked in the interpeptide bridge by their
distant (6 or -y) carboxyl group, and the incorporation
takes place without the participation
of a tRNA derivative. For D-aspartic acid, it
was shown that it is activated as
D-aspartyl-l-phosphate and is incorporated
into a lipid intermediate of the peptidoglycan
of Streptococcus faecium and Lactobacillus
casei (362). The y-linked L- or D- Glu residues
may be synthesized via their y-phosphate derivaties
in analogy to the D-aspartyl residues.
The a-carboxyl group of the dicarboxylic
amino acid is free or it is substituted by an
amide. A typical fragment of the primary
structure of a peptidoglycan of subgroup A4 is
depicted in Fig. 9. As an example, the peptidoglycan
of S. faecium was chosen. As in the case
of subgroup A3, one also finds three variations
in subgroup A4 depending on the diamino acid
occuring in position 3 of the peptide subunit.
The most common variation is A4a with L-Lys
in position 3. The various known peptidoglycan
types of this variation are summarized in Table
9. The peptidoglycan types of the less common
variations A40 and A4-y, containing L-Orn or
m-Dpm, are listed in Table 10.
Group B: cross-linkage between positions 2
and 4. Peptidoglycan group B (cross-linkage
between positions 2 and 4) is much less frequent
than group A. It is found only among some
coryneform bacteria, especially the plant
pathogenic corynebacteria. The cross-linkage
in group B extends from the a-carboxyl group
of o-Glu of one peptide subunit to the carboxyl
group of D-Ala of an adjacent peptide
subunit. Since the cross-linkage occurs between
two carboxyl groups, a diamino acid has
to be present in the interpeptide bridge. This
group also shows the greatest variation in the
composition of the peptide subunit. (i) The
N-terminal amino acid of the peptide subunit
which is bound to the carboxyl group of muramic
acid is not L-Ala as in group A but Gly
or L-Ser. (ii) The D-glutamic acid in position
2 is sometimes hydroxylated and threo-3hydroxyglutamic
acid is found instead of D-
Glu. (iii). The diamino acid at position 3, if
it is present, is not involved in the cross-linkage
and reveals an unsubstituted w-amino
group (in the case of L-Lys and L-Orn) or the
w-amino group is acetylated as in some cases
of L-Dab. In most cases, however, the "unnecessary"
diamino acid in the peptide subunit
is replaced by a monoamino acid such as
L-Hsr, L-Ala, or L-Glu. Typical fragments of
the primary structures of peptidoglycans of
group B are depicted in Fig. 10 and 11. Group
L- Ala
D-Glu- NH2
IEr
-~- - - -
Y NH2
L- Lys --E- D0-Asp.4-
D-Alo
1
D-Ala
L -_____ t
L- Lys
T
FIG. 9. Fragment of the primary structure of a
peptidoglycan of subgroup A4 (Streptococcus faecium,
many lactobacilli). Interpeptide bridge marked
by a dashed frame.
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