I will report on measurements of the elastic properties of two types of 
2D-crystalline shells, microtubules and bacteriophage capsids, probed by 
indentation with a scanning force microscope (SFM).

Both, microtubules and viral capsids are protein shells and we found a
linear elastic regime that can be described by thin-shell theory and
finite element methods. We also found a non-linear regime and catastrophic
collapse under large loads. The mechanical response of these protein
shells at the nanometer scale shows simultaneously aspects of continuum
elasticity, as well as molecular graininess, particularly in their
non-linear behavior.