It is important to identify proline cis/trans isomers that appear in several regulatory
mechanisms of proteins, and to characterize minor species that are present due to
the conformational heterogeneity in intrinsically disordered proteins (IDPs). To obtain
residue level information on these mobile systems we introduce two H-1(alpha)-detected,
proline selective, real-time homodecoupled NMR experiments and analyze the proline
abundant transactivation domain of p53. The measurements are sensitive enough to identify
minor conformers present in 4-15 % amounts; moreover, we show the consequences of
CK2 phosphorylation on the cis/trans-proline equilibrium. Using our results and available
literature data we perform a statistical analysis on how the amino acid type effects
the cis/trans-proline distribution. The methods are applicable under physiological
conditions, they can contribute to find key proline isomers in proteins, and statistical
analysis results may help in amino acid sequence optimization for biotechnological
purposes.
