the presence of different concentrations of aMeMan or
carbohydrate-AuNP as competitive inhibitors. Fig. 2 presents a
set of SPR response curves for Con A in the presence of 6-m-
AuNP. From the inhibition curves of each carbohydrate-AuNP,
its inhibition constant (Ki) is obtained using the equations
derived by Attie et al.19 (Table 1). To compare the inhibition
potencies of the individual mannose ligand on three different m-
AuNP (6-m-AuNP, s-20-m-AuNP or l-20-m-AuNP) with re-
spect to monovalent aMeMan, we calculated the relative
inhibition potency (RIP).20
The RIP values for the mannose ligands of three m-AuNP are
from 11 to 128 (Table 1), indicating that the multivalent
mannose ligands of these m-AuNP have one to two orders
higher affinities to Con A than monovalent mannose ligands. In
addition, all three m-AuNP exhibited a stronger inhibition effect
than 6-g-AuNP and 6-t-AuNP. 6-t-AuNP displayed no detect-
able inhibition effect. This is consistent with the previous
studies that Con A binds to mannose better than glucose but
does not bind to galactose.21,12 Therefore, no switch of Con A
specificity for carbohydrates clustered on nanoparticles was
observed in our system. Taken together, our results demonstrate
that clustering of carbohydrate ligands on a nanoparticle
significantly enhances the ligand binding affinity for lectins,
with no change in lectin binding specificity.
saccharide binding sites are more effective multivalent in-
hibitors than those which fail to engage divalent binding. We
further investigated the effects of different linker lengths of s-
and l-20-m-AuNP on Con A binding affinity (Table 1). The two-
times difference in the RIP values of s- and l-20-m-AuNP might
be attributed to the differences in their intrinsic properties, for
example, the orientation of mannose groups on the surface and/
or the rigidity of the linkers.
In conclusion, we have demonstrated that a nanoparticle can
be a good multivalent ligand carrier. The multivalent inter-
actions between m-AuNP and Con A are affected by nano-
particle size and the linker of mannose ligands. Our approaches
may be also applicable to other types of nanoparticles such as
quantum dots24 and magnetic nanoparticles.
We acknowledge financial supports from the NSC
(91-2120-M-003-001), Academia Sinica, NTNU (ORD-
92-03).
Notes and references
1 Y. C. Lee and R. T. Lee, Acc. Chem. Res., 1995, 28, 321; C. R. Bertozzi
and L. L. Kiessling, Science, 2001, 291, 2357; M. Mammen, S. K. Choi
and G. M. Whitesides, Angew. Chem., Int. Ed., 1998, 37, 2755.
2 J. E. Gestwicki, C. W. Cairo, L. E. Strong, K. A. Oetjen and L. L.
Kiessling, J. Am. Chem. Soc., 2002, 124, 14922.
It has been studied that the Con A tetramer presents two
saccharide binding sites on each face, and the distance between
them is 6.5 nm.22 We compared the inhibition potencies of 6-m-
AuNP and 20-m-AuNP in the SPR competition assays (Table
1). As the particle diameters of 6-m-AuNP and 20-m-AuNP are
comparable to or significantly larger than the distance between
two relevant binding sites on Con A, respectively, the mannose
ligands of 6-m-AuNP are less favorable to engage in the
divalent binding of a Con A tetramer than those of 20-m-
AuNP.23 Our system showed that the carbohydrate ligands with
the ability to span the requisite distance to occupy two Con A
3 P. I. Kitov, H. Shimizu, S. W. Homans and D. R. Bundle, J. Am. Chem.
Soc., 2003, 125, 3284.
4 S. K. Choi, M. Mammen and G. M. Whitesides, J. Am. Chem. Soc.,
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5 R. Roy, D. Page, S. F. Perez and V. V. Bencomo, Glycoconjugate J.,
1998, 15, 251.
6 A. G. Barrientos, J. M. de la Fuente, T. C. Rojas, A. Fernandez and S.
Penades, Chem. Eur. J., 2003, 9, 1909.
7 X. L. Sun, Y. Kanie, C. T. Guo, O. Kanie, Y. Suzuki and C.-H. Wong,
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8 H. Lis and N. Sharon, Chem. Rev., 1998, 98, 637.
9 J. E. Getwicki, L. E. Strong and L. L. Kiessling, Angew. Chem., Int. Ed.,
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10 S. M. Dimick, S. C. Powell, S. A. McMahon, D. N. Moothoo, J. H.
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Soc., 1998, 120, 10575.
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14 M. Brust, M. Walker, D. Betthell, D. J. Schiffrin and R. Whyman, J.
Chem. Soc. Chem. Commun., 1994, 801.
15 6-m-AuNP, s- and l-20-m-AuNP have on average 200, 680 and 840
mannose ligands, respectively, clustered on the nanoparticle surface.
16 L. Nieba, A. Krebber and A. Plückthun, Anal. Biochem., 1996, 234,
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17 M. Mrksich and G. M. Whitesides, Annu. Rev. Biophys. Biomol. Struct.,
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Fig. 2 Inhibition of 0.5 mM Con A binding to the chip by 6-m-AuNP. A set
of inhibition curves for 0, 0.175, 0.5 and 1 mM 6-m-AuNP (top to bottom)
are shown.
19 A. D. Attie and R. T. Raines, J. Chem. Educ., 1995, 72, 119.
20 The RIP of each ligand of m-AuNP is calculated as: Ki(aMeMan)/
[Ki(m-AuNP) 3 the averaged number of mannose ligands on the m-
AuNP].
21 R. W. Weatherman, K. H. Mortell, M. Chervenak, L. L. Kiessling and
E. J. Toone, Biochemistry, 1996, 35, 3619.
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23 The distances between two neighboring mannose groups of m-AuNP are
estimated to be < < 6.5 nm, far closer than that of two binding sites of
Con A tetramer.
24 M. P. Bruchez Jr., M. Moronne, P. Gin, S. Weiss and A. P. Alivisatos,
Science, 1998, 281, 2013; W. C. W. Chan and S. Nie, Science, 1998,
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Table 1 The data of dissociation constants (Ki) and relative inhibition
potency (RIP) of carbohydrate-AuNP to Con A (— no inhibition; / not
determined)
Compound
Ki
RIP
aMeMan
20 3 1024
1.0
6-m-AuNP
s-20-m-AuNP
l-20-m-AuNP
6-g-AuNP
6-t-AuNP
8.8 3 1028
2.3 3 1029
3.5 3 1029
1.6 3 1027
—
11.2
127.8
67.5
/
—
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