In recent years mass spectrometry based techniques have emerged as structural 
biology tools for the characterization of macromolecular, noncovalent 
assemblies. Many of these efforts involve preservation of intact protein 
complexes within the mass spectrometer, providing molecular weight measurements 
that allow the determination of subunit stoichiometry and real-time monitoring 
of protein interactions. Attempts have been made to further elucidate subunit 
architecture through the dissociation of subunits from the intact complex by 
colliding it into inert gas atoms such as argon or xenon. Unfortunately, the 
amount of structural information that can be derived from such strategies is 
limited by the nearly ubiquitous ejection of a single, unfolded subunit. Here, 
we present results from the gas-phase dissociation of protein-protein complexes 
upon collision into a surface. Dissociation of a series of tetrameric and 
pentameric proteins demonstrate that alternative subunit fragments, not observed 
through multiple collisions with gas atoms, can be generated through surface 
collision. Evidence is presented for the retention of individual subunit 
structure, and in some cases, retention of noncovalent interactions between 
subunits and ligands. We attribute these differences to the rapid large energy 
input of ion-surface collisions, which leads to the dissociation of subunits 
prior to the unfolding of individual monomers.