The study by van Pee and co-workers describes the cryo-EM structures of the cholesterol dependent cytolysin (CDC) pneumolysin (PLY) in the membrane-inserted and pre-pore states by single particle and tomography respectively. Although the first crystal structure of a CDC (perfringolysin O) in the water soluble state was solved almost 20 years ago, a high-resolution structure of the membrane-inserted form has been elusive due to the inherent structural heterogeneity of these complexes with the best results so far limited to the resolution of ~10-15Å where domains can be approximately identified but the exact mechanics of the transition from soluble to membrane-inserted cannot be seen. Despite the recent developments of direct electron detectors and better software that have pushed the resolution limits of Cryo-EM, this class of pore forming toxins still poses difficulties due to the irregular size and shape of the pores. In this study authors have succeeded in preparing more homogeneous samples by systematically screening various detergents. The end result is the first near-atomic resolution structure of a CDC in the membrane-inserted state, which provides valuable information for the mechanics of pore formation including the large movements of domains 2 and 3, which have not been resolved previously by other studies. In general the manuscript is well written and is an important step for the field of pore forming proteins of the CDC/MACPF family. Therefore, the three reviewers were overall positive about publishing this work, although several important issues were raised that should be addressed in a revised version.