Department of Immunology, Genentech, South San Francisco, California 94080, USA.
J Biol Chem. 2012 May 4;287(19):15837-50. doi: 10.1074/jbc.M111.286633. Epub 2012 Mar 6.
Paired immunoglobulin-like receptor (PILR) α is an inhibitory receptor that recognizes several ligands, including mouse CD99, PILR-associating neural protein, and Herpes simplex virus-1 glycoprotein B. The physiological function(s) of interactions between PILRα and its cellular ligands are not well understood, as are the molecular determinants of PILRα/ligand interactions. To address these uncertainties, we sought to identify additional PILRα ligands and further define the molecular basis for PILRα/ligand interactions. Here, we identify two novel PILRα binding partners, neuronal differentiation and proliferation factor-1 (NPDC1), and collectin-12 (COLEC12). We find that sialylated O-glycans on these novel PILRα ligands, and on known PILRα ligands, are compulsory for PILRα binding. Sialylation-dependent ligand recognition is also a property of SIGLEC1, a member of the sialic acid-binding Ig-like lectins. SIGLEC1 Ig domain shares ∼22% sequence identity with PILRα, an identity that includes a conserved arginine localized to position 97 in mouse and human SIGLEC1, position 133 in mouse PILRα and position 126 in human PILRα. We observe that PILRα/ligand interactions require conserved PILRα Arg-133 (mouse) and Arg-126 (human), in correspondence with a previously reported requirement for SIGLEC1 Arg-197 in SIGLEC1/ligand interactions. Homology modeling identifies striking similarities between PILRα and SIGLEC1 ligand binding pockets as well as at least one set of distinctive interactions in the galactoxyl-binding site. Binding studies suggest that PILRα recognizes a complex ligand domain involving both sialic acid and protein motif(s). Thus, PILRα is evolved to engage multiple ligands with common molecular determinants to modulate myeloid cell functions in anatomical settings where PILRα ligands are expressed.
配对免疫球蛋白样受体 (PILR)α 是一种抑制性受体，可识别多种配体，包括小鼠 CD99、PILR 相关神经蛋白和单纯疱疹病毒 1 糖蛋白 B。PILRα 与其细胞配体之间相互作用的生理功能以及 PILRα/配体相互作用的分子决定因素尚不清楚。为了解决这些不确定性，我们试图鉴定其他 PILRα 配体，并进一步确定 PILRα/配体相互作用的分子基础。在这里，我们鉴定了两个新的 PILRα 结合伙伴，神经元分化和增殖因子-1 (NPDC1) 和 collectin-12 (COLEC12)。我们发现这些新型 PILRα 配体以及已知 PILRα 配体上的唾液酸化 O-聚糖是 PILRα 结合的必需条件。唾液酸化依赖性配体识别也是唾液酸结合 Ig 样凝集素家族成员 SIGLEC1 的特性。SIGLEC1 Ig 结构域与 PILRα 共享约 22%的序列同一性，该同一性包括一个保守的精氨酸，位于小鼠和人类 SIGLEC1 的位置 97、小鼠 PILRα 的位置 133 和人类 PILRα 的位置 126。我们观察到 PILRα/配体相互作用需要保守的 PILRα Arg-133(小鼠)和 Arg-126(人类)，这与之前报道的 SIGLEC1 Arg-197 在 SIGLEC1/配体相互作用中的要求相对应。同源建模确定了 PILRα 和 SIGLEC1 配体结合口袋之间的惊人相似性，以及半乳糖结合位点中的至少一组独特相互作用。结合研究表明，PILRα 识别涉及唾液酸和蛋白质基序的复杂配体结构域。因此，PILRα 进化为与具有共同分子决定因素的多种配体结合，以调节 PILRα 配体表达的解剖结构中的髓样细胞功能。
