Angiotensin-converting enzyme 2 (ACE2) from raccoon dog can serve as an efficient receptor for the spike protein of severe acute respiratory syndrome coronavirus Lili Xu,1 Yanfang Zhang,1 Yun Liu,1 Zhiwei Chen,2 Hongkui Deng,3 Zhongbin Ma,1 Hualin Wang,1 Zhihong Hu1 and Fei Deng1 Correspondence Fei Deng