Banfield M J, Barker J J, Perry A C, Brady R L
Department of Biochemistry University of Bristol Bristol, BS8 1TD, UK.
Structure. 1998 Oct 15;6(10):1245-54. doi: 10.1016/s0969-2126(98)00125-7.
Proteins belonging to the phosphatidylethanolamine-binding protein (PEBP) family are highly conserved throughout nature and have no significant sequence homology with other proteins of known structure or function. A variety of biological roles have previously been described for members of this family, including lipid binding, roles as odorant effector molecules or opioids, interaction with the cell-signalling machinery, regulation of flowering plant stem architecture, and a function as a precursor protein of a bioactive brain neuropeptide. To date, no experimentally derived structural information has been available for this protein family. In this study we have used X-ray crystallography to determine the three-dimensional structure of human PEBP (hPEBP), in an attempt to clarify the biological role of this unique protein family.
The crystal structures of two forms of hPEBP have been determined: one in the native state (at 2.05 A resolution) and one in complex with cacodylate (at 1.75 A resolution). The crystal structures reveal that hPEBP adopts a novel protein topology, dominated by the presence of a large central beta sheet, and is expected to represent the archaetypal fold for this family of proteins. Two potential functional sites have been identified from the structure: a putative ligand-binding site and a coupled cleavage site. hPEBP forms a dimer in the crystal with a distinctive dipole moment that may orient the oligomer for membrane binding.
The crystal structure of hPEBP suggests that the ligand-binding site could accommodate the phosphate head groups of membrane lipids, therefore allowing the protein to adhere to the inner leaf of bilipid membranes where it would be ideally positioned to relay signals from the membrane to the cytoplasm. The structure also suggests that ligand binding may lead to coordinated release of the N-terminal region of the protein to form the hippocampal neurostimulatory peptide, which is known to be active in the development of the hippocampus. These studies are consistent with a primary biological role for hPEBP as a transducer of signals from the interior membrane surface.
磷脂酰乙醇胺结合蛋白（PEBP）家族的蛋白质在自然界中高度保守，与其他已知结构或功能的蛋白质没有显著的序列同源性。此前已描述了该家族成员的多种生物学作用，包括脂质结合、作为气味效应分子或阿片类物质的作用、与细胞信号传导机制的相互作用、对开花植物茎结构的调节以及作为生物活性脑神经营养肽的前体蛋白的功能。迄今为止，尚无关于该蛋白家族的实验性结构信息。在本研究中，我们使用X射线晶体学来确定人PEBP（hPEBP）的三维结构，以试图阐明这个独特蛋白家族的生物学作用。
已确定两种形式的hPEBP的晶体结构：一种处于天然状态（分辨率为2.05 Å），另一种与二甲胂酸盐复合（分辨率为1.75 Å）。晶体结构表明，hPEBP采用了一种新颖的蛋白质拓扑结构，以一个大的中央β折叠片的存在为主导，预计代表该蛋白家族的原型折叠。从结构中鉴定出了两个潜在的功能位点：一个假定的配体结合位点和一个偶联切割位点。hPEBP在晶体中形成二聚体，具有独特的偶极矩，可能使寡聚体定向以进行膜结合。
hPEBP的晶体结构表明，配体结合位点可以容纳膜脂的磷酸头部基团，因此使该蛋白能够附着在双脂膜的内叶，在那里它将处于理想位置，以便将信号从膜传递到细胞质。该结构还表明，配体结合可能导致蛋白质N端区域的协同释放，以形成海马神经刺激肽，已知该肽在海马体发育中具有活性。这些研究与hPEBP作为内膜表面信号转导器的主要生物学作用一致。
