Long time-scale probing of the protein globular core using hydrogen-exchange and room temperature phosphorescence

Preliminary room temperature phosphorescence measurements of the highly buried Trp109 in E. coli alkaline phosphatase have been used to report on the kinetics of protein hydrogen-deuterium exchange. Upon dilution in D2O the phosphorescence lifetime increases (at 20 degrees C) in a biphasic manner with an immediate change (< 30 seconds) followed by a slow change occurring on an extremely long timescale (days). The immediate D2O-induced lifetime increase is similar to that observed upon dilution into glycerol, a known protein hydrating agent. On the other hand, the slow D2O-induced first order growth in Trp109 lifetime is due to exchange at highly protected protein groups. As the phosphorescence lifetime of Trp109 is dependent on local rigidity, this increase in lifetime reflects changes in alkaline phosphatase structure. This first use of room temperature phosphorescence to monitor proton exchange shows promise as a sensitive and selective probe of protein core dynamics.