We are excited to add a new tool to COSMIC²: ISAC (iterative stable alignment and classification). ISAC performs 2D classification and averaging of single particles, but it approaches this in a different manner than algorithms in RELION or cryoSPARC. A fundamental premise of ISAC is to identify reproducible and stable class averages. This feature of ISAC makes it particularly amenable for performing 2D analysis of negative stain or cryoEM datasets with structurally heterogeneous samples.
For example, the power of ISAC facilitated averaging the flexible dynein motor protein complex (Chowdhury et al. 2015, Supplemental Figure 2):
To help users with this tool, we use RELION extracted particle stacks as inputs and then convert the stack to the appropriate format for running ISAC (EMAN2/Sparx/SPHIRE database files).
Try it out! Please send questions or comments to cosmic2support@umich.edu.