Flexibility between the paramagnetic tag and its protein conjugates is a common yet unresolved issue in the applications of paramagnetic NMR spectroscopy in biological systems. The flexibility greatly attenuates the magnetic anisotropy and compromises paramagnetic effects especially for pseudocontact shift and residual dipolar couplings. Great efforts have been made to improve the rigidity of paramagnetic tag in the protein conjugates, however, the effect of local environment vicinal to the protein ligation site on the paramagnetic effects remains poorly understood. In the present work, the stereospecific effect of chiral tether between the protein and a tag on the paramagnetic effects produced by the tag attached via a D- and L-type linker between the protein and paramagnetic metal chelating moiety was assessed. The remarkable chiral effect of the D- and L-type tether between the tag and the protein on the rigidity of paramagnetic tag is disclosed in a number of protein-tag-Ln complexes. The chiral tether formed between the D-type tag and L-type protein surface minimizes the effect of the local environment surrounding the ligation site on the averaging of paramagnetic tag, which is helpful to preserve the rigidity of a paramagnetic tag in the protein conjugates.

顺磁标签及其蛋白质缀合物之间的灵活性是顺磁核磁共振波谱在生物系统中应用中常见但尚未解决的问题。这种灵活性极大地减弱了磁各向异性并损害了顺磁效应，特别是对于赝接触位移和残余偶极耦合。人们已经做出了巨大的努力来提高蛋白质缀合物中顺磁标签的刚性，然而，蛋白质连接位点附近的局部环境对顺磁效应的影响仍然知之甚少。在本工作中，评估了蛋白质和标签之间的手性系链对通过蛋白质和顺磁性金属螯合部分之间的D型和L型接头连接的标签产生的顺磁性效应的立体特异性效应。在许多蛋白质-标签-Ln复合物中公开了标签和蛋白质之间的D型和L型系链对顺磁性标签的刚性的显着手性效应。 D型标签和L型蛋白质表面之间形成的手性系链最大限度地减少了连接位点周围的局部环境对顺磁标签平均的影响，这有助于保持蛋白质缀合物中顺磁标签的刚性。