Human rhinovirus capsid proteins, molecular model. These are proteins from the capsid (outer protein coat) of rhinovirus 14. Rhinoviruses are responsible for causing about 50% of common colds. Their capsids are formed of four proteins arranged in an icosahedral structure. In this model, the solid colours represent the secondary structure of the proteins (spiral ribbons are alpha helices; arrows are beta sheets), and the faded tubular structure behind represents the individual atoms and bonds.