Tendamistat surface accessibility to the TEMPOL paramagnetic probe

TEMPOL, the soluble spin-label 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-o xyl, has been used to determine the surface characteristics of tendamistat, a small protein with a well-characterised structure both in solution and i n the crystal. A good correlation has been found between predicted regions of exposed protein surface and the intensity attenuations induced by the pr obe on 2D NMR TOCSY cross peaks of tendamistat in the paramagnetic water so lution. All the high paramagnetic effects have been interpreted in terms of more efficient competition of TEMPOL with water molecules at some surface positions. The active site of tendamistat coincides with the largest surfac e patch accessible to the probe. A strong hydration of protein N and C term ini can also be suggested by this structural approach, as these locations e xhibit reduced paramagnetic perturbations. Provided that the solution struc ture is known, the use of this paramagnetic probe seems to be well suited t o delineate the dynamic behaviour of the protein surface and, more generall y, to gain relevant information about the molecular presentation processes.