An international team of scientists has used high-intensity X-ray pulses to determine the structure of the crystalline protein envelope of an insect virus. Their analysis reveals the fine details of the building blocks that make up the viral cocoon down to a scale of 0.2 nanometres (millionths of a millimetre) – approaching atom-scale resolution. The tiny viruses with their crystal casing are by far the smallest protein crystals ever analysed using X-ray crystallography. This opens up new opportunities in the study of protein structures, as the team headed by DESY’s Leading Scientist Henry Chapman from the Center for Free-Electron Laser Science reports in the Proceedings of the National Academy of Sciences (PNAS).