Williams K J, Fuki I V
Dorrance H. Hamilton Research Laboratories, Department of Medicine, Jefferson Medical College of Thomas Jefferson University, Philadelphia, PA 19107-6799, USA.
Curr Opin Lipidol. 1997 Oct;8(5):253-62. doi: 10.1097/00041433-199710000-00003.
Though sometimes regarded as merely passive, space-filling components, proteoglycans are in fact metabolically active molecules with carbohydrate and protein domains that are highly conserved throughout evolution, indicating specific, crucial functions. Here we review recent evidence that heparan sulfate proteoglycans, particularly syndecans and perlecan, are able to mediate directly the internalization of lipoproteins and other ligands, without requiring the participation of LDL receptor family members. Thus, heparan sulfate proteoglycans can function as receptors. In the case of syndecan heparan sulfate proteoglycans, efficient internalization is triggered by clustering of the transmembrane and cytoplasmic domains and then proceeds through a noncoated pit pathway, possibly caveolae. The physiologic and pathophysiologic importance of these direct heparan sulfate proteoglycan-mediated catabolic pathways in the liver and in the arterial wall in vivo remains to be settled.
蛋白聚糖虽然有时仅被视为填充空间的被动成分，但实际上是具有碳水化合物和蛋白质结构域的代谢活跃分子，这些结构域在整个进化过程中高度保守，表明其具有特定的关键功能。在此，我们综述了最近的证据，即硫酸乙酰肝素蛋白聚糖，特别是多配体蛋白聚糖和基底膜聚糖，能够直接介导脂蛋白和其他配体的内化，而无需低密度脂蛋白受体家族成员的参与。因此，硫酸乙酰肝素蛋白聚糖可以作为受体发挥作用。就多配体蛋白聚糖硫酸乙酰肝素而言，跨膜和细胞质结构域的聚集会触发有效的内化，然后通过非包被小窝途径（可能是小窝）进行。这些直接的硫酸乙酰肝素蛋白聚糖介导的分解代谢途径在体内肝脏和动脉壁中的生理和病理生理重要性仍有待确定。
