Scientific Reports 5: Article number: 9451; published online: 30 March 2015; updated: 29 July 2015

The corresponding author is incorrectly given as Yuanfeng Pang rather than Rui Xiao and Shengqi Wang in the HTML version of this Article. For correspondence and requests for materials, please contact Rui Xiao (Ruixiao203@163.com) and Shengqi Wang (sqwang@bmi.ac.cn). This error has now been updated in the original Article.