1dej
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CRYSTAL STRUCTURE OF A DICTYOSTELIUM/TETRAHYMENA CHIMERA ACTIN (MUTANT 646: Q228K/T229A/A230Y/A231K/S232E/E360H) IN COMPLEX WITH HUMAN GELSOLIN SEGMENT 1
OverviewOverview
Replacement of residues 228-230 or 228-232 of subdomain 4 in Dictyostelium, actin with the corresponding Tetrahymena sequence (QTA to KAY replacement:, half chimera-1; QTAAS to KAYKE replacement: full chimera) leads to a, higher Ca(2+)-activation of the regulated acto-myosin subfragment-1 ATPase, activity. The ratio of ATPase activation in the presence of, tropomyosin-troponin and Ca(2+) to that without tropomyosin-troponin, becomes about four times as large as the ratio for the wild-type actin. To, understand the structural basis of this higher Ca(2+)-activation, we have, determined the crystal structures of the 1:1 complex of Dictyostelium, mutant actins (half chimera-1 and full chimera) with gelsolin segment-1 to, 2.0 A and 2.4 A resolution, respectively, together with the structure of, wild-type actin as a control. Although there were local changes on the, surface of the subdomain 4 and the phenolic side-chain of Tyr230 displaced, the side-chain of Leu236 from a non-polar pocket to a more, solvent-accessible position, the structures of the actin chimeras showed, that the mutations in the 228-232 region did not introduce large changes, in the overall actin structure. This suggests that residues near position, 230 formed part of the tropomyosin binding site on actin in actively, contracting muscle. The higher Ca(2+)-activation observed with, A230Y-containing mutants can be understood in terms of a three-state model, for thin filament regulation in which, in the presence of both Ca(2+) and, myosin heads, the local changes of actin generated by the mutation, (especially its phenolic side-chain) facilitate the transition of thin, filaments from a "closed" state to an "open" state. Between 394 and 469, water molecules were identified in the different structures and it was, found that actin recognizes hydrated forms of the adenine base and the Ca, ion in the nucleotide binding site.
DiseaseDisease
Known disease associated with this structure: Amyloidosis, Finnish type OMIM:[137350]
About this StructureAbout this Structure
1DEJ is a Protein complex structure of sequences from Dictyostelium discoideum and tetrahymena thermophila and Homo sapiens with CA and ATP as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Structural basis for the higher Ca(2+)-activation of the regulated actin-activated myosin ATPase observed with Dictyostelium/Tetrahymena actin chimeras., Matsuura Y, Stewart M, Kawamoto M, Kamiya N, Saeki K, Yasunaga T, Wakabayashi T, J Mol Biol. 2000 Feb 18;296(2):579-95. PMID:10669610
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