Knauth Peter, Schlüter Thomas, Czubayko Martin, Kirsch Cornelia, Florian Volker, Schreckenberger Susan, Hahn Heidi, Bohnensack Ralf
Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco (CIATEJ), Av. Normalistas 800, 44270 Guadalajara, México.
J Mol Biol. 2005 Apr 8;347(4):813-25. doi: 10.1016/j.jmb.2005.02.004.
SNX17 is a member of the sorting nexin family (SNX), a group of hydrophilic proteins whose common characteristic property is a phox homology (PX) domain. The PX domain directs SNXs to phosphatidylinositides containing membranes of the endosomal compartment, where the SNXs are involved in the sorting of transmembrane proteins. SNX17 is known to interact with P-selectin and the LDL receptor family. Here, we report that the PX domain of SNX17 specifically binds to phosphatidylinositol 3-phosphate-containing membranes. The functional part of SNX17 that binds P-selectin or Patched (PTCH) consists of a truncated FERM domain and a unique C terminus together (FC-unit). In a yeast two-hybrid analysis a putative recognition motif for the FC-unit was revealed within P-selectin as FxNaa(F/Y). When HepG2 cells overexpress P-selectin together with SNX17, SNX17 changes its distribution from early endosomes to lysobisphosphatidic acid-containing late endosomes. Furthermore, overexpressed SNX17 restrains P-selectin in the outer membrane of the late endosomal compartment, thus preventing the normal lysosomal accumulation of P-selectin. These results suggest that the PX domain is necessary for the intracellular localisation, while the FC-unit is required for cargo recognition. We hypothesise that the expression level of SNX17 may regulate the lysosomal degradation, at least for P-selectin, by suppressing its entry into the inner vesicles of the multi-vesicular bodies (MVBs).
分选连接蛋白17（SNX17）是分选连接蛋白家族（SNX）的成员之一，该家族由一组亲水性蛋白质组成，其共同特征是具有一个吞噬细胞同源（PX）结构域。PX结构域可将SNX引导至内体区室中含有磷脂酰肌醇的膜上，在那里SNX参与跨膜蛋白的分选。已知SNX17可与P-选择素和低密度脂蛋白受体家族相互作用。在此，我们报告SNX17的PX结构域特异性结合含磷脂酰肌醇3-磷酸的膜。SNX17结合P-选择素或 patched（PTCH）的功能部分由一个截短的FERM结构域和一个独特的C末端共同组成（FC单元）。在酵母双杂交分析中，在P-选择素内发现了一个假定的FC单元识别基序为FxNaa(F/Y)。当HepG2细胞同时过表达P-选择素和SNX17时，SNX17的分布从早期内体转变为含溶血双磷脂酸的晚期内体。此外，过表达的SNX17将P-选择素限制在晚期内体区室的外膜中，从而阻止P-选择素正常地在溶酶体中积累。这些结果表明，PX结构域对于细胞内定位是必需的，而FC单元对于货物识别是必需的。我们推测，SNX17的表达水平可能至少通过抑制P-选择素进入多泡体（MVB）的内囊泡来调节其溶酶体降解。
