The article discusses the model structure of monomeric globular (G)-actin and polymerized fibrous (F)-actin. It references a study by T. Oda et al in the 2009 issue of "Nature." It states that the conformation in G-actin results a closed nucleotide-binding cleft and a propeller-like twist of the two domains. It also notes that in F-actin, the conformation of the cleft remains closed and the two domains are untwisted.