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ESSENTIALS OF GLYCOBIOLOGY
LECTURE 21
MAY 7, 2002
Richard D. Cummings, Ph.D.
University of Oklahoma Health Sciences Center
College of Medicine
Oklahoma Center for Medical Glycobiology
“THE S-TYPE LECTINS (GALECTINS)”
The Large and Growing Galectin Family of Lectins
Human Galectin-1
LNHUGB
14.9 kDa Subunit
Human Galectin-2
XP_009968
14.4
Human Galectin-3
(Mac-2 antigen)
XP_007333
27.5
Human Galectin-4
NP_006140
35.5
Rat Galectin-5
NP_037108
16.0
Human Galectin-6
XP_008181
48.8
Human Galectin-7
I55469
15.0
Human Galectin-8
XP_002045
34.9
The Large and Growing Galectin Family of Lectins
Human Galectin-9
XP_006105
XP_006104
35.5 (short form)
39.1 (long form)
Human Galectin-10
XP_009208
15.6
Rat Galectin-11
AAC71765
15.8
(GRIFIN-(Galectin-Related Inter-fiber protein)
Human Galectin-12
AAG40863
AAG40864
AF314686
34.6 (splice variant)
34.5 (splice variant)
Human Galectin-13
NP_037400
15.3
Sheep Galectin-14
Human Urate
Transporter/Channel
17.0
U67958
36.3
Distribution of Galectins
Type
Galectin-1
Galectin-4
Source
h,r,m,
ha;b,p
h,m
h,r,m,
d,ha
h,r,p,m
Galectin-5
r
Galectin-6
Galectin-7
Galectin-8
Galectin-9
m
h,r
h,r
h,r,m
Galectin-10
h
Galectin-11
r
Galectin-2
Galectin-3
Distribution
most tissues
Remarks
Most common and
abundant galectin
small intestine
Minor rel. to Gal-1
macrophage,
N-terminal domain
colon, most tiss. is collagen-like
alimentary tract Linkage of two CRDs is
protease-sensitive
erythrocytes
85% identical to Cterm. CRD of Gal-9
gastrointestinal 85% ident. to Gal-4
skin
marker of stratified epithelia
liver, kidney,lung
thymus, kidney C-terminal domain 85%
Hodgkin’s lymp. identical to Gal-5
eosinophil,
Charcot-Leyden
basophil
crystal protein
lens
(Grifin) may represent a
new lens crystallin,galectinrelated inter-fiber protein
H-human;m-mouse;m-monkey;r-rat;
b-bovine;p-porcine;d-dog;ha-hamster
Conserved Carbohydrate-Recognition Domain of Galectins
F
P
C
M
L
F
G
L
S
V
— H— —N— —R—X —V— R—N— —X —W— E —X— E —X
C
T
4
A
M
Q
5-10
K
V
H
N
I
I
L
N
D L
L Q
P
E I
I E
R
C
N V
G
— K —X — — V —G —X— —X — — —
H
3 K M
3-6 T
M S
E
F
H F
F K
S C
V
Human Galectin-1
69-WGTEQREAV--FPFQPGSVAEVCITFDQANLT---VKLPDGYEFKFPNRL-WGTEQRETV--FPFQKGAPIEITFSINPSDLT---VHLP-GHQFSFPNRL70
Chick-14K Galectin
phylogenetic tree of galectin
family members
percentages of protein identities
among CRDs of human galectin
family members
Crystal Structure (1.7 Å) of Dimeric Human Galectin-1
Crystal Structure (1.7 Å) of Dimeric Human
Galectin-1 With Bound Lactose
Sideview
Turned 90˚
Amino Acids in Human Galectin-1 That Interact with Lactose
N62
N62
W69
E72
W69
E72
H45
R74
H45
R74
H2O
H53
D55
H53
N47
R49
With Lactose
D55
N47
R49
Without Lactose
Biosynthesis of Galectins
Kd ~7mM
Dimer
Kd ~1mM
Glycoprotein
Ligand
?
Monomer
“Metastable
Intermediate”
Inactive
Forms
*
Secretion
Mechanism?
Extracellular
Cytosol
N
Dimer
Monomer
5’
mRNA
3’
SOME PROPOSED FUNCTIONS
OF GALECTINS
Extracellular Galectin
Intracellular Galectin
CELL
CELL
• Cell-cell adhesion
• Cell-matrix interaction
• Cell signaling
Growth arrest
Mitogenesis
Apoptosis
• RNA transport and splicing
• Cytoskeletal organization
Old Galectin Dogma
New Info about Galectins
Require reducing
conditions for activity
Can retain activity without
reducing conditions in presence
of ligands
Occur only as soluble
proteins
Spliced forms may generate
membrane-anchored proteins
Bind terminal Gal
Bind GalNAc, Gal, at internal
and terminal positions, and
sialylated Gal(NAc)
Not post-translationally
modified, other than Nterminal acetylation
Some galectins may be
phosphorylated,
glutathionylated, cross-linked
by transglutaminase
Are galectins always dispersed in the
cytosol and localized in the nucleus?
Galectin-1 is localized to myofibrils of porcine cardiac cells
Acetone Fixed
Frozen Section
Background
Staining:
2 Ab only
(H/E Stained)
1 mAb to
Galectin-1 +
2 Ab
(H/E
Stained)
Background on Galectin-1
Galectin-1 originally isolated from electric organ of
electric eel (called electrolectin) (Teichberg et al,
1975). Subsequently identified in mammalian heart
and lung (de Waard and Kornfeld, 1976) and
embryonic chick muscle (Nowak and Barondes, 1976).
Galectin-1 binds laminin, a basement
glycoprotein(Zhou and Cummings, 1990) lamp
glycoproteins (Do, Smith & Cummings, 1990);
fibronectin (Ozeki, et al, 1995); and a7b1 integrin (Gu et
al, 1994); ganglioside (Kopitz et al, 1998); and CD45
(Perillo et al, 1995).
Galectin-1 (and others) secreted by non-classical
pathway (Hughes, 1994; Cho and Cummings, 1995).
Background on Galectin-1
Galectin-1 is mitogenic for lymphocytes (Pitts and Yang,
1981), but has a growth-inhibitory activity for some
mammalian cells (Wells & Mallucci, 1991) which is
apparently independent of their beta-galactoside binding
site (Scott & Zhang, 2002).
Galectin-1 is able to induce apoptosis in some types of
cells (certain T-cell subsets) (Rappl et al, 2002)
Background on Galectin-1
Galectin-1 activates the neutrophil respiratory burst and
may have proinflammatory functions (Almkvist et al,
2002); activates Ca2+ intracellular rise (Walzel et al,
1996).
Galectin-1 in drosophila is expressed in a
developmentally-regulated tissue- and cell specific
manner (Pace et al, 2002)
Background on Galectin-3
Galectin-3 originally identified as macrophage antigen
Mac-2;and occurs both on the cell surface and
intracellularly.
Upon apoptotic stimulation, galectin 3 becomes
enriched in the mitochondria and prevents
mitochondrial damage and cytochrome c release (Yu et
al, 2002)
Galectin-3 contains the NWGR motif shared by bcl-2
family members; gal3 binds bcl-2 in a lactoseinhibitable manner (Yang et al, 1996; Akahani et al,
1997)
Background on Galectin-3
Galectin-3 suppresses apoptosis (anti-apoptotic) and
anoikis; such suppression may contribute to cell survival
during metastatic cascades; this suppression requires
phosphorylation of Ser6 (Yoshii et al, 2002)
Galectin-3 proposed to play a role in b2-integrinindependent neutrophil extravasation (Sato et al, 2002)
During involution of the mammary gland galectin-3
expression is up-regulated and occurs in non-apoptotic
cells (Mengwasser et al, 2002)
Background on Galectin-3
An alternatively spliced form of chicken galectin-3 contains
a predicted transmembrane spanning domain and leucine
zipper motif (Gorski et al, 2002)
Galectin-3 ligands include Lamp glycoproteins, IgE,
laminin, intestinal mucins, and Mac2 binding protein and
cytokeratin (Goletz et al, 1997).
Background on Galectins-7,-8,and -9
Galectin-7 (also called PIG1) intracellularly expressed exhibits
pro-apoptotic function through JNK activation and
mitochondrial cytochrome c release (Kuwabara et al, 2002)
Galectin-8 expression is inversely related to tumour growth
rate (Nagy et al, 2002)
Galectin-9 (also known as ecalectin) represents a novel class
of eosinophil chemoattractants (ECAs) produced by activated
T cells (Sato et al, 2002; Matsumoto et al, 2002)
Further Background on Galectins
Intracellularly, galectins may exist in a glutathionylated form
(Fratelli et al, 2002)
Galectin-14 expressed in eosinophils and its release may
contribute to eosinophil function and allergic inflammation
(Dunphy et al, 2002)
Galectins-1, -3, and -14 contain a Bcl-2-like motif; through this
motif these galectins may regulate apoptosis (38-41). In
particular, it has been postulated that Bcl-2 and galectin-3
may heterodimerize through this motif to inhibit Fas-antibodymediated apoptosis (Yang et al, 1996; Akahani et al, 1997;
Perillo et al, 1997).
Further Background on Galectins
Many galectins have already been linked to immunity
(Vasta, et al, 1999).
Galectins regulate cytokine production (Cortegano et al,
19989; Vespa et al, 1999), stimulate thymocyte apoptosis
(Galectin-1; Chung et al,2000; Pace et al 2000; Galectin9 - Wada et al, 1997), activate respiratory bursts of
neutrophils and mast cells (Yamaoka et al, 1995); and
migration of leukocytes (Matsushita et al, 2000; Sano, et
al, 2000).
Galectins 1, 3, 10, 11 and 14 appear to localize
simultaneously to the nucleus and cytoplasm under
various conditions (Dunphy, et al, 2000).
Further Background on Galectins
The role galectins play in the nucleus remains
unclear, but it has been postulated that galectins 1
and 3 regulate pre-mRNA splicing (Dagher et al,
1995; Vyakarnam et al, 1998; Dunphy et al, 2000).
The specific presence of galectin-14 in eosinophils
and its release during inflammatory reactions into the
lung fluid indicate that the protein may play an
important role in allergic-type responses, in particular
in allergic asthma (Dunphy et al, 2002).
Unexpectedly, the C-terminus of the human urate
transporter/channel contains the galectin CRD
(related to galectin-5) in a transmembrane protein
(Leal-Pinto et al, 1997).
Information about Galectin Function from Mouse Genetics
Galectin 3(-/-) mice develop fewer inflammatory cell
infiltrations in the peritoneal cavities than the wild-type
(gal3(+/+)) mice in response to inflammatory stimuli,
mainly due to lower numbers of macrophages (m).
Also, when compared to cells from gal3(+/+) mice,
thioglycollate-elicited inflammatory cells from gal3(-/-)
mice exhibited significantly lower levels of NF-kappaB
response.
Information about Galectin Function from Mouse Genetics
Different cell-spreading phenotypes are observed in
cultured (m) from the two genotypes; (m) from
gal3(+/+) mice exhibited well spread out morphology,
those from gal3(-/-) mice were often spindle-shaped.
Peritoneal (m) from gal3(-/-) mice are more prone
to undergo apoptosis than those from gal3(+/+) mice
when treated with apoptotic stimuli (Hsu et al, 2000).
Information about Galectin Function from Mouse Genetics
Galectin 1(-/-) mice have generally normal phenotypes
and litter sizes ().
Galectin 1(-/-) mice have disrupted axonal architecture
for a subset of olfactory neurons (Puche et al, 1996);
this is supported by in vitro work which showed that
galectin-1 promotes binding between olfactory neurons
and a laminin glycoconjugate that lines the axonal
migration path in vivo (Mahanthappa et al, 1994).
In vitro galectin-1 can induce programmed cell death in
T-cells in a CD45-dependent manner (Perillo et al,
1995).