School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
PLoS One. 2012;7(7):e41924. doi: 10.1371/journal.pone.0041924. Epub 2012 Jul 26.
Integrins are signal transducer proteins involved in a number of vital physiological processes including cell adhesion, proliferation and migration. Integrin molecules are hetero-dimers composed of two distinct subunits, α and β. In humans, 18 α and 8 β subunits are combined into 24 different integrin molecules. Each of the subunit comprises a large extracellular domain, a single pass transmembrane segment and a cytosolic tail (CT). The CTs of integrins are vital for bidirectional signal transduction and in maintaining the resting state of the receptors. A large number of intracellular proteins have been found to interact with the CTs of integrins linking integrins to the cytoskeleton.
METHODOLOGY/PRINCIPAL FINDINGS: In this work, we have investigated structure and interactions of CTs of the leukocyte specific integrin αXβ2. We determined the atomic resolution structure of a myristoylated CT of αX in perdeuterated dodecylphosphocholine (DPC) by NMR spectroscopy. Our results reveal that the 35-residue long CT of αX adopts an α-helical conformation for residues F4-N17 at the N-terminal region. The remaining residues located at the C-terminal segment of αX delineate a long loop of irregular conformations. A segment of the loop maintains packing interactions with the helical structure by an extended non-polar surface of the αX CT. Interactions between αX and β2 CTs are demonstrated by (15)N-(1)H HSQC NMR experiments. We find that residues constituting the polar face of the helical conformation of αX are involved in interactions with the N-terminal residues of β2 CT. A docked structure of the CT complex indicates that a network of polar and/or salt-bridge interactions may sustain the heteromeric interactions.
CONCLUSIONS/SIGNIFICANCE: The current study provides important insights into the conservation of interactions and structures among different CTs of integrins.
整合素是参与许多重要生理过程的信号转导蛋白，包括细胞黏附、增殖和迁移。整合素分子是由两个不同亚基α和β组成的异二聚体。在人类中，18 个α和 8 个β亚基组合成 24 种不同的整合素分子。每个亚基都包含一个大的细胞外结构域、一个单一的跨膜片段和一个胞质尾（CT）。整合素的 CT 对于双向信号转导和维持受体的静止状态至关重要。已经发现大量的细胞内蛋白与整合素的 CT 相互作用，将整合素与细胞骨架连接起来。
方法/主要发现：在这项工作中，我们研究了白细胞特异性整合素αXβ2 的 CT 的结构和相互作用。我们通过 NMR 光谱法测定了一个豆蔻酰化的αX CT 在全氘化十二烷基磷酸胆碱（DPC）中的原子分辨率结构。我们的结果表明，35 个残基长的αX CT 在 N 端区域的 F4-N17 采用α-螺旋构象。αX 的 C 端区域的其余残基描绘了一个长的不规则构象环。环的一段通过αX CT 的扩展非极性表面与螺旋结构保持堆积相互作用。（15）N-（1）H HSQC NMR 实验证明了αX 和β2 CT 之间的相互作用。我们发现构成αX 螺旋构象极性面的残基与β2 CT 的 N 端残基相互作用。CT 复合物的对接结构表明，极性和/或盐桥相互作用网络可能维持异源二聚体相互作用。
结论/意义：本研究为不同整合素 CT 之间相互作用和结构的保守性提供了重要的见解。
