Biomedical Engineering Reference
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OH
NH
2
OH
O
O
NH
2
3
O
O
HO
HO
O
O
O
O
HO
HO
Cl
Cl
HO
HO
O
O
O
O
Cl
Cl
HO
OH
HO
OH
O
O
O
O
O
O
N
N
N
N
N
H
2
N
H
2
O
H
N
O
H
N
N
N
H
H
O
H
H
H
H
O
O
O
O
O
N
N
O
O
H
H
O
H
2
N
O
H
2
N
OH
OH
OH
OH
O
O
HO
H
O
HO
O
N
O
R
H
O
R
H
O
O
O
1
2
Fig. 1 Comparison of interactions between Vancomycin (3) with normal (1) and mutated (2)
bacterial cell wall-forming peptide sequence. An attractive hydrogen bond is replaced for a
repulsive electrostatic interaction, thus decreasing the affinity of the antibiotic by a factor of 1,000
4
6
OH
O
OH
O
OH
H
2
N
O
NH
O
O
H
N
AA
1
AA
2
AA
3
O
H
2
NOC
N
NH
2
O
L-Disc
N
N
N
O
O
O
H
+
H
N
H
N
H
O
O
H
NH
2
N
N
H
N
H
O
O
+
O
O
H
2
N
OH
-
O
O
O
H
N
H
2
N
O
NH
N
H
O
OH
O
O
N
H
L-Tpi
H
N
8
O
5
7
AA
1-3
= L/D: Arg, Asn, His, Leu, N-Me-Leu, Lys, Phe, N-Me-Phe, Pro, Thr, Trp, Tyr, Tic
L: Aib, Chg, Atc, Dapa, Disc, Isn, Tpi, N-Me-Gly
34 × 34 × 34 = 39,304 receptors
Fig. 2 Schematic representation of receptor library 4 for the substrate
N
,
N
0
-Ac
2
-
L
-Lys-
D
-Ala-
D
-
Lac-OH (5) (
left
) and receptor of highest affinity 8 with the amino acid sequence
L
-N-Me-Phe-
L
-
Disc-
L
-Tyr (
right
)
of Vancomycin: the right part corresponding to a simplified carboxylate binding
pocket, which should be able to bind to both
D
-Ala-OH and
D
-Lac-OH via three
hydrogen bonds. The left side of the receptor, on the other hand, consists of a variable
tripeptide, which is free to rotate and should therefore be able to avoid electrostatic
repulsion between the antibiotic's carbonyl group and the lactate oxygen. Indeed, an
on-bead screening with a fluorescently labeled substrate revealed binding constants
five times as high as for Vancomycin. The best receptors mainly contained the amino
acid sequence
L
-Tpi-
L
-His (29%) and
L
-N-Me-Phe-
L
-Disc (20%) in position AA
1
and
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