Department of Biochemistry, Faculty of Biology, Complutense University, 28040 Madrid, Spain; Research Institut "Hospital 2 de Octubre (imas12)", 28040 Madrid, Spain.
Department of Macromolecular Structures, National Center of Biotechnology, CSIC, 28049 Madrid, Spain.
J Mol Biol. 2018 May 11;430(10):1495-1509. doi: 10.1016/j.jmb.2018.03.027. Epub 2018 Apr 4.
Pulmonary surfactant protein D (SP-D) is a glycoprotein from the collectin family that is a component of the lung surfactant system. It exhibits host defense and immune regulatory functions in addition to contributing to the homeostasis of the surfactant pool within the alveolar airspaces. It is known that the SP-D monomer forms trimers, which further associate into higher-order oligomers. However, the pathway and the interactions involved in the assembly of SP-D oligomers are not clearly understood. In the current study, a recombinant form of full-length human SP-D (rhSP-D) has been qualitatively and quantitatively studied by atomic force microscopy (AFM) and electrophoresis, with the aim to understand the conformational diversity and the determinants defining the oligomerization of the protein. The rhSP-D preparation studied is a mixture of trimers, hexamers, dodecamers and higher-order oligomeric species, with dodecamers accounting for more than 50% of the protein by mass. Similar structures were also found in hSP-D obtained from proteinosis patients, with the largest fuzzy-ball-like oligomers being more abundant in these samples. The proportion of dodecamer is increased under acidic conditions, accompanied by a conformational change into more compact configurations. Two hexamers appear to be the minimal necessary unit for dodecamer formation, with stabilization of the dodecamer occurring via non-covalent, ionic, and hydrophobic interactions between the individual N-terminal domains and the proximal area of the SP-D collagen stems.
肺表面活性物质蛋白 D（SP-D）是一种来自凝集素家族的糖蛋白，是肺表面活性物质系统的组成部分。除了有助于肺泡气腔中表面活性物质池的动态平衡外，它还具有宿主防御和免疫调节功能。已知 SP-D 单体形成三聚体，这些三聚体进一步缔合成更高阶的寡聚物。然而，SP-D 寡聚物组装的途径和相互作用尚不清楚。在本研究中，通过原子力显微镜（AFM）和电泳对全长人 SP-D（rhSP-D）的重组形式进行了定性和定量研究，旨在了解该蛋白的构象多样性和决定其寡聚化的因素。所研究的 rhSP-D 制剂是三聚体、六聚体、十二聚体和更高阶寡聚体的混合物，按质量计，十二聚体占蛋白质的 50%以上。在来自蛋白病患者的 hSP-D 中也发现了类似的结构，这些样品中最大的模糊球样寡聚物更为丰富。在酸性条件下，十二聚体的比例增加，同时构象发生变化，变得更加紧凑。两个六聚体似乎是形成十二聚体的最小必需单位，通过单体的 N 端结构域和 SP-D 胶原主干近端区域之间的非共价、离子和疏水相互作用稳定十二聚体的形成。
