 |
PDBsum entry 1zmh
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Antimicrobial protein
|
PDB id
|
|
|
|
1zmh
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Reconstruction of the conserved beta-Bulge in mammalian defensins using d-Amino acids.
|
|
|
Authors
|
|
C.Xie,
A.Prahl,
B.Ericksen,
Z.Wu,
P.Zeng,
X.Li,
W.Y.Lu,
J.Lubkowski,
W.Lu.
|
|
|
Ref.
|
|
J Biol Chem, 2005,
280,
32921-32929.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
Defensins are cationic antimicrobial mini-proteins that play important roles in
the innate immune defense against microbial infection. Six invariant Cys
residues in each defensin form three structurally indispensable intramolecular
disulfide bridges. The only other residue invariant in all known mammalian
defensins is a Gly. Structural studies indicate that the invariant Gly residue
is located in an atypical, classic-type beta-bulge with the backbone torsion
angles (Phi, Psi) disallowed for L-amino acids but permissible for
D-enantiomers. We replaced the invariant Gly17 residue in human neutrophil
alpha-defensin 2 (HNP2) by L-Ala or one of the D-amino acids Ala, Glu, Phe, Arg,
Thr, Val, or Tyr. Although L-Ala17-HNP2 could not be folded, resulting in
massive aggregation, all of the D-amino acid-substituted analogs folded with
high efficiency. The high resolution x-ray crystal structures of dimeric
D-Ala17-HNP2 were determined in three different crystal forms, showing a well
preserved beta-bulge identical to those found in other defensins. The seven
D-analogs of HNP2 exhibited highly variable bactericidal activity against
Gram-positive and Gram-negative test strains, consistent with the premise that
interplay between charge and hydrophobicity dictates how amphiphilic defensins
kill. Further, the bactericidal activity of these d-amino acid analogs of HNP2
correlated well with their ability to induce leakage from large unilamellar
vesicles, supporting membrane permeabilization as the lethal event in microbial
killing by HNP2. Our findings identify a conformational prerequisite in the
beta-bulge of defensins essential for correct folding and native structure,
thereby explaining the molecular basis of the Gly-Xaa-Cys motif conserved in all
mammalian defensins.
|
|
|
|
|
|
|
|
Figure 1.
FIGURE 1. Amino acid sequence alignment of mammalian  -defensins from human,
mouse, rhesus macaque, rabbit, guinea pig, and rat
(us.expasy.org/sprot). The invariant residues, including six Cys
and Gly17 (HNP1 numbering), are shaded in black. The boxed
residues, Arg5 and Glu13, form a salt bridge in the structure
and are highly conserved.
|
|
Figure 7.
FIGURE 7. The hydrogen-bonding pattern of the  -bulge in
a representative dimer of D-Ala^17-HNP2.
|
|
|
|
|
|
The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2005,
280,
32921-32929)
copyright 2005.
|
|
|
|
|
|
|
