Abstract
In her Perspective, [Holmes][1] discusses the elucidation of a crystal structure reported by [ Li et al. ][2] (in the same issue) of the receptor-binding domain of the SARS coronavirus spike glycoprotein bound to its human receptor, angiotensin-converting enzyme 2 (ACE2). The structure reveals how only a few of the many contacting amino acids in the large interface between the spike protein and receptor are critical determinants of the host range of coronavirus binding and entry. [1]: http://www.sciencemag.org/cgi/content/full/309/5742/1822 [2]: http://www.sciencemag.org/cgi/content/short/309/5742/1864