Spectroscopy, Dynamics, and Hydration of S-Nitrosylated Myoglobin.

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 are 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 agrees with experimental findings on other proteins as is the observation of buried -SNO. For MbSNO the observed relocation of the EF loop in the simulations by ∼3 Å 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 compared with -SH, MbSNO recruits more water molecules in the first two hydration shells due to stronger electrostatic interactions. 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.