 |
PDBsum entry 2zgn
|
|
|
|
References listed in PDB file
|
 |
|
Key reference
|
|
|
Title
|
|
Structural basis for the tumor cell apoptosis-Inducing activity of an antitumor lectin from the edible mushroom agrocybe aegerita.
|
|
|
Authors
|
|
N.Yang,
D.F.Li,
L.Feng,
Y.Xiang,
W.Liu,
H.Sun,
D.C.Wang.
|
|
|
Ref.
|
|
J Mol Biol, 2009,
387,
694-705.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
|
|
|
Abstract
|
|
|
Lectin AAL (Agrocybe aegerita lectin) from the edible mushroom A. aegerita is an
antitumor protein that exerts its tumor-suppressing function via
apoptosis-inducing activity in cancer cells. The crystal structures of
ligand-free AAL and its complex with lactose have been determined. The AAL
structure shows a dimeric organization, and each protomer adopts a prototype
galectin fold. To identify the structural determinants for antitumor effects
arising from the apoptosis-inducing activity of AAL, 11 mutants were prepared
and subjected to comprehensive investigations covering oligomerization
detection, carbohydrate binding test, apoptosis-inducing activity assay, and
X-ray crystallographic analysis. The results show that dimerization of AAL is a
prerequisite for its tumor cell apoptosis-inducing activity, and both galactose
and glucose are basic moieties of functional carbohydrate ligands for lectin
bioactivity. Furthermore, we have identified a hydrophobic pocket that is
essential for the protein's apoptosis-inducing activity but independent of its
carbohydrate binding and dimer formation. This hydrophobic pocket comprises a
hydrophobic cluster including residues Leu33, Leu35, Phe93, and Ile144, and is
involved in AAL's function mechanism as an integrated structural motif. Single
mutants such as F93G or I144G do not disrupt carbohydrate binding and
homodimerization capabilities, but abolish the bioactivity of the protein. These
findings reveal the structural basis for the antitumor property of AAL, which
may lead to de novo designs of antitumor drugs based on AAL as a prototype model.
|
|
|
|
|
|
|
|
Figure 2.
Fig. 2. The carbohydrate recognition site of AAL. (a) The
dimer structure of the rAAL–lactose complex. The lactose and
sulfate ions bound to the CRD concave of AAL are shown in a
ball-and-stick model. (b) The electrostatic potential map on the
rAAL surface showing a positively charged cavity bound with
lactose. (c) The carbohydrate recognition site bound with
lactose. Residues of AAL and lactose involved in recognition are
shown. The F[o ]− F[c] omit electron density map is calculated
without the ligand and contoured at 3.0σ. (d) The interactions
between lactose and AAL. A total of 10 hydrogen bonds are
involved in contacts between six residues and lactose. Residues
Asn43, His59, Asn72, and Trp80 are involved in galactose moiety
reorganization, whereas residue Arg85 is involved in glucose
moiety, and Arg63 and Glu83 contact both galactose and glucose
moieties. In these figures, lactose, sulfate ion, and residues
involved in recognition are represented as a ball-and-stick
model.
|
|
Figure 5.
Fig. 5. The structure of a unique hydrophobic pocket found in
the F–S cavity of AAL. (a) Structural alignment of AAL (main
chains in green and side chains in magenta) and galectin-1
(blue; PDB code 1LSA). It shows a structurally homologous cavity
between the F and S β-sheet layers in which a functionally
important hydrophobic pocket is identified in galectin-1. (b)
The hydrophobic pocket resided in the F–S cavity of AAL, which
consists of two hydrophobic residue clusters, LLFI (Leu33,
Leu35, Phe93, and Ile144; in magenta) and FLV (F28, Leu47, and
Val102; in cyan). (c) The unique LLFI cluster adopted an
integrated structural organization.
|
|
|
|
|
|
The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2009,
387,
694-705)
copyright 2009.
|
|
|
|
|
|
|
