  A quantum-mechanical (QM) method rooted on density functional theory (DFT)
has been employed to determine conformations of the methane-thiosulfonate spin
label (MTSL) attached to a fragment extracted from the activation loop of
Aurora-A kinase. The features of the calculated energy surface revealed low
energy barriers between isoenergetic minima and the system could be described
in a population of 76 rotamers that can be also considered for other systems
since it was found that the X3, X4 and X5 do not depend on the previous two
dihedral angles. Conformational states obtained were seen to comparable to
those obtained in the {\alpha}-helix systems studied previously, indicating
that the protein backbone does not affect the torsional profiles significantly
and suggesting the possibility to use determined conformations for other
protein systems for further modelling studies.
