Center for Integrated Protein Science Munich at the Department Chemie, Technische Universität München, 85748 Garching, Germany.
Division of Genetics and Cell Biology, Università Vita-Salute IRCCS Ospedale San Raffaele, 20132 Milano, Italy.
Proc Natl Acad Sci U S A. 2017 Oct 10;114(41):E8575-E8584. doi: 10.1073/pnas.1701797114. Epub 2017 Sep 27.
Professional secretory cells can produce large amounts of high-quality complex molecules, including IgM antibodies. Owing to their multivalency, polymeric IgM antibodies provide an efficient first-line of defense against pathogens. To decipher the mechanisms of IgM assembly, we investigated its biosynthesis in living cells and faithfully reconstituted the underlying processes in vitro. We find that a conserved peptide extension at the C-terminal end of the IgM heavy (Ig-μ) chains, termed the tailpiece, is necessary and sufficient to establish the correct geometry. Alanine scanning revealed that hydrophobic amino acids in the first half of the tailpiece contain essential information for generating the correct topology. Assembly is triggered by the formation of a disulfide bond linking two tailpieces. This induces conformational changes in the tailpiece and the adjacent domain, which drive further polymerization. Thus, the biogenesis of large and topologically challenging IgM complexes is dictated by a local conformational switch in a peptide extension.
专业分泌细胞能够产生大量高质量的复杂分子，包括 IgM 抗体。由于 IgM 抗体的多价性，多聚 IgM 抗体为病原体提供了有效的第一道防线。为了解析 IgM 组装的机制，我们研究了其在活细胞中的生物合成，并在体外忠实地重建了潜在的过程。我们发现，IgM 重链（Ig-μ）C 末端的保守肽延伸，称为尾部，对于建立正确的几何形状是必需和充分的。丙氨酸扫描显示，尾部前半部分的疏水性氨基酸包含产生正确拓扑结构的必要信息。组装是由连接两个尾部的二硫键形成引发的。这会引起尾部和相邻结构域的构象变化，从而推动进一步的聚合。因此，大型和拓扑挑战性 IgM 复合物的生物发生由肽延伸中的局部构象开关决定。
