The goal of structural biology is to elucidate the structure of bio-macromolecules in atomic detail. Until now, the method of choice was X-ray crystallography. However, its bottleneck is the preparation of diffraction quality crystals. Recently, a new method was developed, the cryo-electron microscopy (cryoEM) that relies on imaging individual molecules using electrons . CryoEM can reach the atomic resolution by combining imagines of thousands of molecules, however, it is itself limited by the size of the sample analyzed. Too small (<100 kDa) bio-molecules are difficult to align to access the atomic resolution. We plan to prepare virus like particles (VLPs) and pentamers of viral major capsid protein (VP1) derived from mouse polyomavirus that would harbor target small proteins. In order to produce a versatile system, such a small protein would be an antibody fragment such as the cameloid nanobody that would be targeted against the protein of interest. Prepared VLPs and pentamers will be analyzed using cryoEM and protein crystallography to demonstrate their ability as a useful tool for structural analysis of small proteins in cryoEM. Up until now, we were able to design, optimize and crystallize a stable protein complex of VP1 pentamer with CFP fused to truncated VP3.