PMC:2724026 / 28076-29018 JSONTXT

{"project":"2_test","denotations":[{"id":"19362094-15690348-62520542","span":{"begin":199,"end":201},"obj":"15690348"},{"id":"19362094-15533036-62520543","span":{"begin":221,"end":226},"obj":"15533036"},{"id":"19362094-12547210-62520544","span":{"begin":289,"end":291},"obj":"12547210"},{"id":"19362094-15935381-62520545","span":{"begin":321,"end":325},"obj":"15935381"},{"id":"19362094-16678203-62520546","span":{"begin":676,"end":678},"obj":"16678203"},{"id":"19362094-11214326-62520546","span":{"begin":676,"end":678},"obj":"11214326"}],"text":"Formation of the central core of FADD involves packing of a four-helix bundle. Several other four-helix bundle proteins have been studied in detail by Φ-value analysis; two members of the ACBP family51 and apocytochrome b56252 (which are up-down helical bundles) and Im7, the homologous Im98 and the FF domain of HYPA/FBP1153 (which have three long helices plus a shorter helix). In all these cases, formation of the TS involves packing of three helices with one helix being essentially unstructured. It has been suggested that the early, obligatory stages in nucleation of folding will be formation of the interactions that are necessary to establish the overall topology.54–56 Packing of three helices in a simple four-helix bundle is sufficient to establish the topology. It seems probable that the more complex Greek key topology of the DD requires all four central elements to be assembled, as was found in the Ig-like Greek key domains."}