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STD NMR
, _4 D r* S4 h2 HSTD NMR 6 A+ A2 M* j$ ]7 m% B3 G
experiments detect magnetization that is transferred from a receptor protein 5 r1 H8 {" y/ s! P' F' o( A
to a bound ligand. Only bound ligands show STD effects. The experiment may be 2 a5 S. L' `9 z; H* E
combined with virtually any other NMR experiment, and therefore is well suitable ' d" \) Y/ O- |
to tackle even very complex problems. In particular, in combination with multidimensional 5 P+ T5 ~' S. v" `% L3 @
NMR a full characterization of a bound ligand out of a mixture is straightforward.
" u# Z {% H: R! \5 q STD NMR is extremely robust and gives maximal effects at protein to ligand ratios * f9 a1 ?6 {$ l9 [0 n4 ~
greater than ca. 1:100. It follows that less than 1 nmol of protein is necessary
, |- S+ j v N for screening. With the availability of so called cryo probes it will be possible ; d9 L1 O* ]. S% d
to work with hundred pmol amounts of protein. The dissociation constant should - }" }% C% I/ q2 Q7 f8 h
be in the range between nM and mM. Therefore, STD NMR covers at least two orders
1 |+ Z" P, }$ {7 q* ?2 y& X8 J of magnitudes more for dissociation constants than trNOE experiments. From competitive
/ V4 W: i! k- H& H5 n/ P" G STD experiments dissociation constants may be derived. 5 v2 S! u. o7 b

# X% G1 k; E& s5 M) F% W K, c * n/ d( F' q+ `6 _% {- [
Schematic 4 V# ]" J- a& O! R0 O* Q
display of the STD NMR effect. Saturation of the protein leads to a direct saturation - ~ I: c# ?, K& H1 e
of those parts of ligand(s) in direct contact to the protein. By exchange between ) D6 n4 E1 W- j, _
bound and free state the saturation is transported to solution and detected
7 K, A$ s' f# }1 u, Y: X by subtracting a spectrum with saturation from a normal spectrum. / B5 J; E2 b( l3 v
STD NMR gives precise information about the binding epitope of the ligand. This
, v5 [1 }" X' c: M' A is very important information for the design of a potent drug. The optimal drug
! I5 A! c% h4 s. c' J Q, m is of optimal size and optimal shape. The size is deduced from STD NMR, and
" v, |3 F; |, W) G, ]9 } the shape is delivered by trNOE experiments.
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