Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 30013, Taiwan.
J Biol Chem. 2013 May 10;288(19):13522-33. doi: 10.1074/jbc.M113.455329. Epub 2013 Mar 27.
CXCL4L1 is a highly potent anti-angiogenic and anti-tumor chemokine, and its structural information is unknown.
CXCL4L1 x-ray structure is determined, and it reveals a previously unrecognized chemokine structure adopting a novel C-terminal helix conformation.
The alternative helix conformation enhances the anti-angiogenic activity of CXCL4L1 by reducing the glycosaminoglycan binding ability.
Chemokine C-terminal helix orientation is critical in regulating their functions. Chemokines, a subfamily of cytokines, are small, secreted proteins that mediate a variety of biological processes. Various chemokines adopt remarkable conserved tertiary structure comprising an anti-parallel β-sheet core domain followed by a C-terminal helix that packs onto the β-sheet. The conserved structural feature has been considered critical for chemokine function, including binding to cell surface receptor. The recently isolated variant, CXCL4L1, is a homologue of CXCL4 chemokine (or platelet factor 4) with potent anti-angiogenic activity and differed only in three amino acid residues of P58L, K66E, and L67H. In this study we show by x-ray structural determination that CXCL4L1 adopts a previously unrecognized structure at its C terminus. The orientation of the C-terminal helix protrudes into the aqueous space to expose the entire helix. The alternative helix orientation modifies the overall chemokine shape and surface properties. The L67H mutation is mainly responsible for the swing-out effect of the helix, whereas mutations of P58L and K66E only act secondarily. This is the first observation that reports an open conformation of the C-terminal helix in a chemokine. This change leads to a decrease of its glycosaminoglycan binding properties and to an enhancement of its anti-angiogenic and anti-tumor effects. This unique structure is recent in evolution and has allowed CXCL4L1 to gain novel functional properties.
CXCL4L1 是一种高效的抗血管生成和抗肿瘤趋化因子，但其结构信息尚不清楚。
确定了 CXCL4L1 的 X 射线结构，揭示了一种以前未被识别的趋化因子结构，采用了新的 C 端螺旋构象。
通过降低糖胺聚糖结合能力，替代的螺旋构象增强了 CXCL4L1 的抗血管生成活性。
趋化因子 C 端螺旋构象在调节其功能方面至关重要。趋化因子是细胞因子的一个亚家族，是一种小的分泌蛋白，介导多种生物学过程。各种趋化因子采用显著保守的三级结构，包括一个反平行的β-折叠核心结构域，后面是一个 C 端螺旋，螺旋堆积在β-折叠上。保守的结构特征被认为是趋化因子功能的关键，包括与细胞表面受体结合。最近分离的变体 CXCL4L1 是 CXCL4 趋化因子（或血小板因子 4）的同源物，具有很强的抗血管生成活性，仅在 P58L、K66E 和 L67H 三个氨基酸残基上有所不同。在这项研究中，我们通过 X 射线结构测定表明，CXCL4L1 在其 C 端采用了以前未被识别的结构。C 端螺旋的取向突出到水相空间，暴露整个螺旋。替代的螺旋构象改变了整个趋化因子的形状和表面特性。L67H 突变主要负责螺旋的摆动效应，而 P58L 和 K66E 的突变仅起次要作用。这是首次观察到趋化因子中 C 端螺旋呈开放构象。这种变化导致其糖胺聚糖结合特性降低，并增强其抗血管生成和抗肿瘤作用。这种独特的结构是进化中的新事物，使 CXCL4L1 获得了新的功能特性。
