Viruses are finely tuned to perform their deadly job. Many viruses are highly specific: they infect only a particular animal or plant, and may even only infect a few types of cells within their preferred hosts. However, viruses occasionally cross the line, and gain the ability to infect other hosts. This is often termed viral emergence, and has been sensationalized as a major threat to global health in books such as The Hot Zone. Fortunately, this type of switching occurs only rarely, but when it does, it can be a disaster. For instance, several of the largest historic pandemics of influenza have been caused by emergence of human viruses from bird viruses. An even more recent viral emergence has occurred in the parvoviruses, where a cat virus suddenly mutated and caused a global pandemic disease in dogs. About the RCSB PDB Molecule of the Month Using selected molecules from the PDB archive, each feature includes an introduction to the structure and function of the molecule, a discussion of its relevance to human health and welfare, and suggestions for viewing and accessing further details. The RCSB PDB Molecule of the Month is read by students, teachers, and scientists worldwide at www.pdb.org. This May 2010 edition was written an
