Mortenson David E, Kreitler Dale F, Yun Hyun Gi, Gellman Samuel H, Forest Katrina T
Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
Acta Crystallogr D Biol Crystallogr. 2013 Dec;69(Pt 12):2506-12. doi: 10.1107/S090744491302444X. Epub 2013 Nov 19.
The human Pin1 WW domain is a small autonomously folding protein that has been useful as a model system for biophysical studies of β-sheet folding. This domain has resisted previous attempts at crystallization for X-ray diffraction studies, perhaps because of intrinsic conformational flexibility that interferes with the formation of a crystal lattice. Here, the crystal structure of the human Pin1 WW domain has been obtained via racemic crystallization in the presence of small-molecule additives. Both enantiomers of a 36-residue variant of the Pin1 WW domain were synthesized chemically, and the L- and D-polypeptides were combined to afford diffracting crystals. The structural data revealed packing interactions of small carboxylic acids, either achiral citrate or a D,L mixture of malic acid, with a mobile loop region of the WW-domain fold. These interactions with solution additives may explain our success in crystallization of this protein racemate. Molecular-dynamics simulations starting from the structure of the Pin1 WW domain suggest that the crystal structure closely resembles the conformation of this domain in solution. The structural data presented here should provide a basis for further studies of this important model system.
人Pin1 WW结构域是一种小的自主折叠蛋白，已成为用于β-折叠生物物理研究的模型系统。该结构域一直阻碍着之前用于X射线衍射研究的结晶尝试，这可能是由于内在的构象灵活性干扰了晶格的形成。在此，人Pin1 WW结构域的晶体结构通过在小分子添加剂存在下的外消旋结晶获得。化学合成了Pin1 WW结构域36个残基变体的两种对映体，并将L-和D-多肽混合以得到衍射晶体。结构数据揭示了小羧酸（非手性柠檬酸或苹果酸的D,L混合物）与WW结构域折叠的一个可移动环区域之间的堆积相互作用。这些与溶液添加剂的相互作用可能解释了我们在该蛋白质外消旋体结晶方面取得成功的原因。从Pin1 WW结构域的结构开始的分子动力学模拟表明，晶体结构与该结构域在溶液中的构象非常相似。此处给出的结构数据应为进一步研究这个重要的模型系统提供基础。
