Table 1. Simulations, force fields and salt bridge stabiliy.

The table shows the stability of each of the three salt bridges, reported as the population of structures with N–O distances shorter than 5 Å, in each of the eight different combinations of force field and water models.

Force field	Water model	dmax	Population
			K12–E23	K39–D35	K58–D55
CHARMM22∗	TIPS3P	13.5 Å	0.73	0.42	0.61
CHARMM22∗	TIP3P	13.5 Å	0.67	0.20	0.61
CHARMM27	TIPS3P	13.5 Å	0.83	0.14	0.75
Amber ff03w	TIP4P/2005	13.5 Å	0.60	0.48	0.81
Amber ff99SB∗-ILDN	TIP3P	13.5 Å	0.63	0.72	0.98
OPLS AA	SPC/E	13.5 Å	0.65	0.39	0.98
a99SB-disp	TIP4P-D	13.0 Å	0.67	0.25	0.68
AMBER ff15ipq	SPC/Eb	14.0 Å	0.096	0.20	0.02