We next examined the conformational preferences of the amino acid side chains by analyzing their χ 1 and χ 2 angle distributions. As can be seen in Figure , all of the residues appear to sample 3 states (with varying preferences for those states) that are either gauche or trans with respect to rotation about the Cα-Cβ bond. ff99SB yields nearly identical χ 1 distributions for each unmodified amino acid and its phosphorylated variants, with the greatest exception being unmodified threonine (THR) vs. phosphorylated threonine (T1P and TPO).