MTSL (''S''-(1-oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl)methyl methanesulfonothioate) is an
organosulfur compound
Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfu ...
that is used as a
nitroxide spin label.
[Christian Altenbach, Kyoung-Joon Oh, René J. Trabanino, Kálmán Hideg, Wayne L. Hubbell "Estimation of Inter-Residue Distances in Spin Labeled Proteins at Physiological Temperatures: Experimental Strategies and Practical Limitations" Biochemistry, 2001, volume 40, pp 15471–15482. ] MTSL is
bifunctional, consisting of the nitroxide and the thiosulfonate ester
functional groups. The nitroxide label is sterically protected, so it is relatively unreactive.
Labeling
MTSL is attached to proteins by reaction with thiol groups. The reaction exploits standard reactivity of thiosulfate esters.
Methanesulfinate (CH
3SO
2−) is the leaving group:
:RSO
2S-''nitroxide'' + ''protein''-SH → ''protein''-S-S-''nitroxide'' + RSO
2H
The
heterodisulfide
In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups ...
bond to the
cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile.
When present as a deprotonated catalytic residue, sometime ...
residue is robust, enabling site-directed spin labelling.
[Berliner, L.J., Grunwald, J., Hankovszky, H.O., Hideg, K. (1982). A novel reversible thiol-specific spin label: papain active site labeling and inhibition. Analytical Biochemistry 119, 450-455. ] The MTSL moiety will add 184.3
daltons to the mass of the
protein or
peptide to which it is attached. The cysteine can be introduced using
site-directed mutagenesis, and hence most positions in a protein can be labelled.
Spectroscopy
In
Nuclear magnetic resonance the introduction of the paramagnetic group increases the relaxation rate of nearby
nuclei.
[ Its presence can be detected as peak broadening and loss of intensity in peaks corresponding to nearby nuclei. Hence proximity can be inferred for all nuclei, that are affected. A major advantage of this method over traditional methods for obtaining distance restraints in protein NMR is the increased length, as paramagnetic relaxation enhancement can detect distances up to 25 Å (2.5 nm) as opposed to about 6 Å (0.6 nm) using the nuclear Overhauser effect. Spin labelling with MTSL is frequently used in investigation of residual structure in intrinsically unstructured proteins.
]
References
{{DEFAULTSORT:Mtsl
Pyrrolines
Amine oxides