Lassoued K, Illges H, Benlagha K, Cooper M D
Department of Medicine, University of Alabama at Birmingham, 35294, USA.
J Exp Med. 1996 Feb 1;183(2):421-9. doi: 10.1084/jem.183.2.421.
Biosynthesis of the immunoglobulin (Ig) receptor components and their assembly were examined in cell lines representative of early stages in human B lineage development. In pro-B cells, the nascent surrogate light chain proteins form a complex that transiently associates in the endoplasmic reticulum with a spectrum of unidentified proteins (40, 60, and 98 kD) and Bip, a heat shock protein family member. Lacking companion heavy chains, the surrogate light chains in pro-B cells do not associate with either the Ig(alpha) or Ig(beta) signal transduction units, undergo rapid degradation, and fail to reach the pro-B cell surface. In pre-B cells, by contrast, a significant portion of the surrogate light chain proteins associate with mu heavy chains, Ig(alpha), and Ig(beta) to form a stable receptor complex with a relatively long half-life. Early in this assembly process, Bip/GRP78, calnexin, GRP94, and a protein of approximately 17 kD differentially bind to the nascent mu heavy chains. The 17-kD intermediate is gradually replaced by the surrogate light chain protein complex, and the Ig(alpha) and Ig(beta) chains bind progressively to the mu heavy chains during the complex and relatively inefficient process of pre-B receptor assembly. The results suggest that, in humans, heavy chain association is essential for surrogate light chain survival and transport to the cell surface as an integral receptor component.
在代表人类B淋巴细胞发育早期阶段的细胞系中，对免疫球蛋白（Ig）受体成分的生物合成及其组装过程进行了研究。在前B细胞中，新生的替代轻链蛋白形成一种复合物，该复合物在内质网中与一系列未鉴定的蛋白质（40kD、60kD和98kD）以及热休克蛋白家族成员Bip短暂结合。由于缺乏伴侣重链，前B细胞中的替代轻链既不与Ig(α) 也不与Ig(β) 信号转导单位结合，会迅速降解，无法到达前B细胞表面。相比之下，在pre-B细胞中，相当一部分替代轻链蛋白与μ重链、Ig(α) 和Ig(β) 结合，形成一种具有相对较长半衰期的稳定受体复合物。在这个组装过程的早期，Bip/GRP78、钙连接蛋白、GRP94和一种约17kD的蛋白质分别与新生的μ重链结合。17kD的中间体逐渐被替代轻链蛋白复合物取代，在pre-B受体组装的复杂且相对低效的过程中，Ig(α) 和Ig(β) 链逐渐与μ重链结合。结果表明，在人类中，重链结合对于替代轻链的存活以及作为完整受体成分转运到细胞表面至关重要。
