Backbone dynamics and hydrogen exchange of Pseudomonas aeruginosa ferricytochrome c 551

A model-free analysis of Pseudomonas aeruginosa ferricytochrome c(551) dynamics based on (15)N R(1), (15)N R(2), and (1)H]-(15)N heteronuclear nuclear Overhauser effect data is reported. The protein backbone is highly rigid (< S(2)>=0.924+/-0.005) and displays little variation in picosecond-nanosecond time scale dynamics over the structure. The loop structure containing the axial methionine ligand (loop 3) displays anomalous rigidity, which is attributed to its high proline content. Also reported are protection factors calculated from hydrogen-exchange rates. These data reveal that loop 3 residues, including the axial methionine, are protected from exchange as a result of long-range hydrogen-bonding interactions. These results are contrasted with data reported for Saccharomyces cerevisiae iso-1-ferricytochrome c, which displays higher overall flexibility (< S(2)>=0.80+/-0.07), greater variation of dynamics as a function of structure, and low protection factors for loop 3. This analysis reveals that heme proteins with similar functions and topologies may display diverse dynamical properties.