An endosomal sorting complex required for transport. Consists of two soluble subcomplexes of highly charged coiled-coil proteins and is required for sorting and/or concentration of multivesicular body (MVB) cargoes. [ http://www.ncbi.nlm.nih.gov/pubmed/12900393 http://www.ncbi.nlm.nih.gov/pubmed/12892785 ]