Bastian A, Kratzin H, Eckart K, Hilschmann N
Max-Planck-Institut für experimentelle Medizin, Abteilung Immunchemie, Göttingen, Germany.
Biol Chem Hoppe Seyler. 1992 Dec;373(12):1255-63. doi: 10.1515/bchm3.1992.373.2.1255.
All intra J chain disulfide bridges of human sIgA, the disulfide bonds between the J chain and the two IgA monomers, and one inter IgA monomer disulfide bridge were determined. sIgA was isolated from colostrum of healthy women and digested with IgA1-specific protease followed by cyanogen bromide cleavage. This procedure generated fragments of 140 kDa, 60 kDa, and 28 kDa. The 28-kDa polypeptide comprised the complete J chain covalently bound to two alpha 1 chain octapeptides derived from the C-termini of two alpha 1 chains. The 28-kDa fragment was digested with trypsin. The resulting peptides were purified by RP-HPLC, and subsequently characterized by amino-acid analysis, mass spectrometry, and gas phase sequencing. These data unequivocally show that the J chain cysteines C1-C6, C4-C5, and C7-C8 form intra chain disulfide bridges. The second (C2) and the third (C3) J chain cysteines are disulfide linked to two alpha chain cysteines (C17) joining the two IgA monomers of sIgA tail to tail. The remaining two alpha chains of the two monomers are directly bound to each other via their ultimate cysteines (C17-C17). A new model for the J chain in sIgA is presented.
确定了人分泌型IgA（sIgA）中所有J链内二硫键、J链与两个IgA单体之间的二硫键以及一个IgA单体间二硫键。从健康女性初乳中分离出sIgA，先用IgA1特异性蛋白酶消化，然后用溴化氰裂解。该过程产生了140 kDa、60 kDa和28 kDa的片段。28 kDa的多肽包含完整的J链，该J链与源自两条α1链C末端的两个α1链八肽共价结合。用胰蛋白酶消化28 kDa的片段。所得肽段通过反相高效液相色谱（RP-HPLC）纯化，随后通过氨基酸分析、质谱和气相测序进行表征。这些数据明确表明，J链半胱氨酸C1-C6、C4-C5和C7-C8形成链内二硫键。J链的第二个（C2）和第三个（C3）半胱氨酸通过二硫键与连接sIgA两个IgA单体尾对尾的两个α链半胱氨酸（C17）相连。两个单体的其余两条α链通过它们的末端半胱氨酸（C17-C17）直接相互结合。提出了sIgA中J链的新模型。
