ER chaperones use a protein folding and quality control glyco-code

N-glycans act as quality control tags by recruiting lectin chaperones to assist protein maturation in the endoplasmic reticulum. The location and composition of N-glycans (glyco-code) are key to the chaperone-selection process. Serpins, a class of serine protease inhibitors, fold non-sequentially to achieve metastable active states. Here, the role of the glyco-code in assuring successful maturation and quality control of two human serpins, alpha-1 antitrypsin (AAT) and antithrombin III (ATIII), is described. We find that AAT, which has glycans near its N terminus, is assisted by early lectin chaperone binding. In contrast, ATIII, which has more C-terminal glycans, is initially helped by BiP and then later by lectin chaperones mediated by UGGT reglucosylation. UGGT action is increased for misfolding-prone disease variants, and these clients are preferentially glucosylated on their most C-terminal glycan. Our study illustrates how serpins utilize N-glycan presence, position, and composition to direct their proper folding, quality control, and trafficking.

Detection and characterization of a lambda gt11 recombinant clone of M. leprae that expresses an antigenic determinant of a 64-kDa protein

A genomic library of Mycobacterium leprae in the expression vector lambda gt11 was screened with rabbit polyclonal hyperimmune antiserum elicited with a sonicated extract of M. leprae. Numerous reactive clones were isolated by this immunoscreening, indicating a broad antibody response of the rabbit. None of the recombinant clones was reactive with monoclonal antibodies to the previously well-characterized M. leprae recombinant clones. One of the clones isolated, clone A, encoded a large, 132-143-kDa beta-galactosidase fusion protein expressing an epitope of M. leprae. Monospecific antibodies eluted from this fusion protein reacted on Western blots with a 64-kDa M. leprae protein. The DNA of this clone was shown to be distinct from the gene encoding the well-characterized immunodominant 65-kDa protein by DNA hybridization. We have identified a new lambda gt11 recombinant clone encoding a fusion protein with a 64-kDa protein. This protein is recognized by the humoral immune response of the rabbit in response to a challenge with an M. leprae cell extract.