Unmasking a two-faced protein

Abstract

Single-molecule fluorescence spectroscopy and molecular dynamics simulations illuminate the structure and dynamics of PSD-95, a protein involved in neural plasticity.

Keywords: E. coli; molecular biophysics; neuroscience; postsynaptic density; protein dynamics; single molecule fluorescence; single-molecule FRET; structural biology.

Figure 1.. Synaptic localization, structure and dynamics of protein PSD-95.

(A) Protein PSD-95 (shown as five circles of different colors on a line) mediates protein-protein interactions in the postsynaptic density (other proteins are shown as grey circles or black squares) and hence modulates signal transduction in neurons (neurotransmitters are shown in green being released from the pre-synaptic cell). (B) Domain structure of PSD-95, showing the five domains of the protein (with the PDZ domains shown in light blue, the SH3 domain shown in orange and the GuK domain shown in pink). The PSG supramodule is indicated. (C) The PSG supramodule switches quickly between two conformations in which the PDZ3 domain (shown in light blue with a dashed red border) takes different positions. (D) High-speed recording of structural data overcomes averaging of distinct protein conformations. Top: when observed at 10 frames per second (fps), the positions of the SH3 and GuK domains (which remain still) are correctly resolved, but the PDZ3 domain is switching between its positions in the two conformations of the PSG supramodule faster than the images are being taken. This results in an ‘average’ conformation being recorded (shown in blue) instead of the two ‘real’ conformations with the correct positions of the PDZ3 domain (red dashed circles). Center: when observed at 100 fps, a similar thing happens, but in this case two (incorrect) averaged conformations are observed. Bottom: 1000 fps is a high enough frame rate to correctly resolve the two conformations of the PSG supramodule. Observed averaged conformations are shown in blue and marked with an arrowhead; true underlying conformations are shown as red dashed circles.