N-syndecan: structure and function of a transmembrane heparan sulfate proteoglycan.

D J Carey
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Abstract

N-syndecan is a member of the syndecan family of transmembrane heparan sulfate proteoglycans that was cloned initially from neonatal rat Schwann cells and is the principal syndecan expressed during early postnatal development in the central and peripheral nervous systems. Purified N-syndecan binds in vitro with high affinity to several extracellular regulatory ligands, including basic fibroblast growth factor, the secreted adhesive protein heparin binding growth-associated molecule, and a novel collagen-like protein secreted by Schwann cells. These extracellular ligands utilize the heparan sulfate chains of N-syndecan for binding. Based on the striking amino acid sequence homology of the cytoplasmic domain of N-syndecan to syndecan-1, it is proposed that N-syndecan associates with the actin-based cytoskeleton. N-syndecan core proteins self associate by means of an unusual dimerization motif comprised of the transmembrane domain and a short flanking sequence in the ectodomain. Similar to other single transmembrane domain receptor proteins, it is suggested that ligand-regulated dimerization of N-syndecan represents a mechanism for regulating downstream signaling activities. In rat brain tissue a significant fraction of the N-syndecan molecules are present in a soluble form, presumably as a result of proteolytic membrane shedding. A model is presented for morphoregulatory activity of N-syndecan in which extracellular ligand-induced clustering of N-syndecan molecules on the cell surface promotes cytoskeletal association and reorganization. Membrane shedding separates the functional domains of the proteoglycan and terminates this activity.

N-syndecan:一种跨膜硫酸肝素蛋白多糖的结构和功能。
N-syndecan是跨膜硫酸肝素蛋白多糖syndecan家族的成员,最初是从新生大鼠雪旺细胞中克隆出来的,是出生后早期中枢和周围神经系统表达的主要syndecan。纯化的N-syndecan在体外以高亲和力结合多种细胞外调节配体,包括碱性成纤维细胞生长因子、分泌的粘附蛋白肝素结合生长相关分子和一种由雪旺细胞分泌的新型胶原样蛋白。这些细胞外配体利用N-syndecan的硫酸肝素链进行结合。基于N-syndecan的胞质结构域与syndecan-1惊人的氨基酸序列同源性,提出N-syndecan与基于肌动蛋白的细胞骨架相关。N-syndecan核心蛋白通过一个不寻常的二聚化基序自我结合,该二聚化基序由跨膜结构域和外结构域的短侧翼序列组成。与其他单跨膜结构域受体蛋白类似,研究表明配体调节的N-syndecan二聚化是调节下游信号活动的一种机制。在大鼠脑组织中,N-syndecan分子的很大一部分以可溶性形式存在,可能是由于蛋白水解膜脱落的结果。提出了N-syndecan的形态调控活性模型,其中细胞外配体诱导的N-syndecan分子在细胞表面聚集促进细胞骨架结合和重组。膜脱落分离了蛋白多糖的功能域并终止了这种活性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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