Chemistry Reference
In-Depth Information
Figure 26.1
- and
- Defensins. Six human
by solid lines. A dashed line indicates a salt
bridge in HNP-1-3. ARMAD5 is from the nine-
banded armadillo, a basal mammal, and OPAD1
is from the opossum, a marsupial. Gaps (
α
β
- defensins (HNP - 1 - 4 and HD - 5 and - 6) and
three human
α
- defensins (HBD - 1 - 3) are shown.
Conserved residues are boxed. Cysteine resi-
dues are numbered, and their pairing is shown
β
−
)
were introduced to maximize the alignments.
Ehrlich, who called attention to the polymorphic shape of the cell's nucleus and
the neutrophilic (neither acidophilic nor basophilic) staining properties of its
granules. The six
-defensins of rabbit PMNs are even more abundant, accounting
for over 15% of the cell's total protein. The PMNs of cattle and fowl lack
α
α
- defen-
sins, but contain multiple
β
-defensins. Mice (but not rats), pigs, sheep and horses
have PMNs that lack
-defensins. Instead, these PMNs contain other anti-
microbial peptides, including many that belong to the cathelicidin family.
Figure 26.1 shows three human
α
- and
β
- defensins (HBD - 1 - 3), plus one each from the
zebrafi sh (
Danio
) and the chicken (Gal 2). The existence of defensins in a basal
mammal, the armadillo, and the opossum, a marsupial, indicates that the lineage
of
β
α
-defensins extends back at least around 135 million years.
β
- Defensins are at
least 300 million years older than
α
-defensins, judging from their presence in
zebrafi sh. The
-defensin peptides have several structural differences.
Whereas Cys1 pairs with Cys6 in
α
- and
β
- defensins.
Their inter-cysteine spacing also differs, with a single residue between Cys1 and
Cys2 in
α
-defensins, it pairs with Cys5 in
β
α
- defensins, and fi ve or six intervening residues in
β
- defensins. In con-
trast, Cys4 and Cys5 are more widely separated in
- defensins. These reciprocal
deletions and insertions permit Cys1-Cys6 pairing in
α
α
- defensins, but eliminate
the short,
- defensins. Much more ancient
defensin-like peptides also exist (see Info Box 1); however, their genetic kinship
to the defensins mentioned above is uncertain.
α
-helical segment found in many
β
