  S-nitrosylation, the covalent addition of NO to the thiol side chain of
cysteine, is an important post-transitional modification that can alter the
function of various proteins. The structural dynamics and vibrational
spectroscopy of S-nitrosylation in the condensed phase is investigated for the
methyl-capped cysteine model system and for myoglobin. Using conventional point
charge and physically more realistic multipolar force fields for the -SNO group
it is found that the SN- and NO-stretch and the SNO-bend vibrations can be
located and distinguished from the other protein modes for simulations of MbSNO
at 50 K. The finding of stable cis- and trans-MbSNO is consistent with
experiments on other proteins as is the observation of buried -SNO. For MbSNO
the observed relocation of the EF loop in the simulations by $\sim 3$ \AA\/ is
consistent with the available X-ray structure and the conformations adopted by
the -SNO label are in good overall agreement with the X-ray structure. Despite
the larger size of the -SNO group, MbSNO is found to recruit more water
molecules within 10 \AA\/ of the modification site than WT Mb due to the
stronger electrostatics. Similarly, when comparing the hydration between the A-
and H-helices they differ by up to 30 \% between WT and MbSNO. This suggests
that local hydration can also be significantly modulated through nitrosylation.
