Yeast ISW1a is classified as a member of the Imitation SWItch (ISWI) subgroup of the SWI2/SNF2 superfamily of ATP-dependent chromatin remodelers.The main function of ISW1a is the repression of gene expression through modulation of nucleosome positioning.ISW1a is a hetero-dimeric complex comprised of the 135 KDa Isw1 subunit and the 94 KDa Ioc3 subunits.Isw1 contains an N-terminal ATPase domain connected by a linker to a C-terminal domain which is composed of three consecutive subdomains HAND, SANT and SLIDE (HSS).The Ioc3 protein does not share any significant sequence homology to any structually characterized domain.We have solved the crystal structure of ISW1a (DATPase) complex both with and without bound duplex DNA at resolutions of 3.60 (P6 5 22) and 3.25 (H32) Å, respectively [1].In both structures, there is one ISW1a complex in the asymmetric unit.In terms of biological significance, these structures revealed not only an entirely new protein fold architecture of Ioc3 carrying a novel recognition motif for a specific DNA sequence, but also SANT and SLIDE were proven to take topologically unique DNA binding forms.Of interest to crystallographers, the ISW1a crystal in the absence of DNA displayed resolution improvements after introducing point mutations which increased salt bridging in the crystal packing interface, and ISW1a-DNA crystal also exhibited the improvements only after applying dehydration and slow cooling techniques during the post crystal treatment.Taking both these results into account, the introduction of a point mutation at the crystal packing interface and the dehydration and slow cooling methodologies could represent more general tools to improve resolution for poorly diffracting crystals.
原文链接
分享
引用
