Session: Parallel session 6 - Instrumental development

Atomic resolution molecular imaging by scanning probe and electron microscopy based on soft-landing electrospray ion beam deposition.

Electrospray ion beam deposition (ESIBD), the deposition of intact molecular ions created by electrospray ionisation onto solid surfaces in vacuum, has been introduced in our lab as a tool for the handling of large and complex, usually non-volatile molecules (see Fig. A).[1]  Initially, the high-resolution single-molecule imaging by scanning probe microscopy (SPM) has been the major application. Here ESIBD proved successful in the in-ves¬tigation of structure, conformation, and properties of proteins, peptides, sac¬charides, and synthetic mo¬le-cules (see Fig. CD).[2,3]  



ESIBD's high level of control over molecular ion beam and environment opens new avenues in molecular ima-ging. Native ESI enables the chem¬i¬cally selective enrich¬ment of folded proteins and proteins complexes for structural in¬ves¬ti¬gation by electron microscopy imaging (cryoEM)[4,5], and low en¬er¬gy electron holo¬gra¬phy (LEEH, Fig. F).



Optimized conditions for native deposition promote imaging of individual proteins at a res¬o¬lu¬tion sufficient for the con¬struc¬tion of atomic models from cryoEM data (see Fig. B).[5]  The structure ob¬¬tained from cryoEM after embedding the landed proteins in ice grown from the gas phase shows a fold and subunit arrangement which is remarkably similar to the solution structure.  Small conformational changes cause differences mostly at the protein surface and interfaces. We find the closing of cavities and crevices’ due to self-interaction in absence of water, a change readily reversed in MD simulations to find the native solution structure.