PMC:2724026 / 3725-4673 JSONTXT

{"project":"2_test","denotations":[{"id":"19362094-15504411-62520512","span":{"begin":271,"end":273},"obj":"15504411"},{"id":"19362094-15504412-62520512","span":{"begin":271,"end":273},"obj":"15504412"},{"id":"19362094-16618492-62520512","span":{"begin":271,"end":273},"obj":"16618492"},{"id":"19362094-15504412-62520513","span":{"begin":690,"end":692},"obj":"15504412"},{"id":"19362094-16618492-62520514","span":{"begin":946,"end":948},"obj":"16618492"}],"text":"In contrast to the complex Greek key topology of the Ig-like domains, spectrin domains are simple three-helix coiled-coil structures with up-down-up connectivity. Three spectrin domains have been studied in our laboratory (R15, R16 and R17 from chicken brain α-spectrin).16–18 In all three of these proteins, two elements of secondary structure (helices A and C) form and interact early and the third (helix B) forms and packs after the rate-determining transition state. There is some suggestion of a change in mechanism, as is seen in the homeodomain family; R16 folds by a framework-like mechanism, with secondary structure (especially in helix C) preceding tertiary structure formation,17 whereas R15 folds by a nucleation condensation mechanism with secondary and tertiary structure forming concomitantly (our unpublished results). R17 shows a mechanism similar to that of R16, but with higher Φ-values and more helical structure in helix A.18"}