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STD NMR
. m3 y- X) U( u) U/ R* rSTD NMR
( O0 ~# ~ m7 \$ D, P experiments detect magnetization that is transferred from a receptor protein . |5 B- B5 F5 p! w$ p9 ~
to a bound ligand. Only bound ligands show STD effects. The experiment may be
' {6 ?, k4 [, F. ?- v6 K# J0 e combined with virtually any other NMR experiment, and therefore is well suitable , G9 X& W- ]3 j
to tackle even very complex problems. In particular, in combination with multidimensional
/ p5 g( z k% k6 m/ g; p+ c: @+ ]; T NMR a full characterization of a bound ligand out of a mixture is straightforward.
2 k$ p$ N9 s1 D3 o/ ~0 j STD NMR is extremely robust and gives maximal effects at protein to ligand ratios
$ v1 w. ~. \( O& X greater than ca. 1:100. It follows that less than 1 nmol of protein is necessary 7 g" V/ a% ]4 U! z9 D
for screening. With the availability of so called cryo probes it will be possible G& {* }, Q! b
to work with hundred pmol amounts of protein. The dissociation constant should 5 W5 T8 l5 c4 n) d: g+ V1 u
be in the range between nM and mM. Therefore, STD NMR covers at least two orders 3 R6 }0 F F4 d, o! F& Z9 e
of magnitudes more for dissociation constants than trNOE experiments. From competitive 7 P/ ?/ A6 R2 ?0 m7 ~
STD experiments dissociation constants may be derived. : _$ w7 M9 w6 v- r; |* j7 c/ c
 % l* h8 h' j9 Q: i! [! o/ c
" z+ M) Q7 {( Z% x4 F Schematic 1 P" `, u! A. d% c
display of the STD NMR effect. Saturation of the protein leads to a direct saturation " O' L/ B1 X9 F9 ^
of those parts of ligand(s) in direct contact to the protein. By exchange between ( L2 k2 J5 a7 y% h
bound and free state the saturation is transported to solution and detected
% U4 U9 x3 w6 f# B: z9 B+ r by subtracting a spectrum with saturation from a normal spectrum. & R5 U. ?- e; [+ ~# c. {8 g
STD NMR gives precise information about the binding epitope of the ligand. This
5 ~$ P7 D3 o; _0 Z is very important information for the design of a potent drug. The optimal drug 6 C G0 n! i$ `& p0 f
is of optimal size and optimal shape. The size is deduced from STD NMR, and / s; r. S* \: ~* J; I6 y) e4 J8 R {
the shape is delivered by trNOE experiments.
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