How low can we go? Structure determination of small biological complexes using single particle cryo EM

•Biological complexes with molecular weights of <100kDa can be resolved to high resolution using single-particle cryo-EM.•Advances in sample grid freezing and imaging technologies can maximize the signal-to-noise ratio in images of small targets.•High-resolution structures of small targets can be obtained using conventional defocus imaging•Small complexes can be visualized at 200 or 300keV.•Structures of challenging membrane proteins can be determined de novo.