Recombinant human thyroid peroxidase produced in insect cells has similar properties to native human thyroid peroxidase

Purification of recombinant human thyroid peroxidase (hTPO) from AD293 mammalian cells

Human thyroid peroxidase (hTPO) has been secretory expressed in AD293 mammalian cells. cDNA sequence of 'Gluc' (Gaussia luciferase) protein from Gaussia princeps was incorporated at the amino terminal of hTPO gene for secretion of targeted protein outside the mammalian cells. Augmentation of TPO clone in serum free mediums was investigated and a simplified purification procedure of hTPO has been reported here. Purified hTPO was further analyzed by SDS-PAGE and immunoblotting (western blotting). The relative molecular mass of hTPO was found to be 105kDa. This is the first report with respect to cost effective and simplified purification approach to get highest yield and purity of recombinant hTPO.

Role of sulfated tyrosines of thyroglobulin in thyroid hormonosynthesis

Our previous studies showed that sulfated tyrosines (Tyr-S) are involved in thyroid hormone synthesis and that Tyr(5), the main hormonogenic site of thyroglobulin (Tg), is sulfated. In the present paper, we studied the role of Tyr-S in the formation and activity of the peroxidase-Tg complex. Results show that noniodinated (35)SO(3)-Tg specifically binds (Kd=1.758 microM) to immobilized lactoperoxidase (LPO) via Tyr-S linkage by using saturation binding and competition experiments. We found that NIFEY-S, a 15-amino acid peptide corresponding to the NH2-end sequence of Tg and containing the hormonogenic acceptor Tyr5-S, was a better competitor than cholecystokinin and Tyr-S. 35SO3-Tg, iodinated without peroxidase, bound to LPO with a Kd (1.668 microM) similar to that of noniodinated Tg, suggesting that 1) its binding occurs via Tyr-S linkage and 2) Tyr-S requires peroxidase to be iodinated, whereas nonsulfated Tyr does not. Iodination of NIFEY-S with [125I]iodide showed that Tyr5-S iodination increased with LPO concentration, whereas iodination of a nonsulfated peptide containing the donor Tyr130 was barely dependent on LPO concentration. Enzymatic hydrolysis of iodinated Tg or NIFEY-S showed that the amounts of sulfated iodotyrosines also depended on LPO amount. Sulfated iodotyrosines were detectable in the enzyme-substrate complex, suggesting they have a short life before the coupling reaction occurs. Our data suggest that after Tyr-S binding to peroxidase where it is iodinated, the sulfate group is removed, releasing an iodophenoxy anion available for coupling with an iodotyrosine donor.

Point-of-care assays for autoantibodies to thyroid peroxidase and to thyroglobulin

Point-of-care (POC) assays for autoantibodies to thyroid peroxidase (TPOAb) and to thyroglobulin (TgAb) are described. Both assays are based on the ability of autoantibodies in test samples (whole blood, plasma, or sera) to inhibit the binding of monoclonal antibodies to TPO or to Tg. The assays require no special equipment and give results in 10 minutes. Analysis of samples from healthy blood donors (n = 80), patients with autoimmune thyroid disease (n = 97) and nonthyroid autoimmune diseases (n = 20) showed that results with the POC tests compared well to those obtained by agglutination assay and enzyme-linked immunosorbent assay (ELISA). The reference immunoprecipitation assays (IPA) based on 125I-labeled TPO or Tg were more sensitive than the POC tests particularly in the case of TgAb measurements. However, no samples were found positive by POC test and negative by IPA emphasizing the high specificity of the POC assays. Our results suggest that POC testing for TPOAb and TgAb with assays such as those we describe could be useful in certain situations. These include prediction of postpartum thyroiditis and the development of interferon-alpha-related thyroid disease.

X-ray crystal structure of a monoclonal antibody that binds to a major autoantigenic epitope on thyroid peroxidase

Thyroid peroxidase (TPO) catalyzes the production of thyroid hormones and is a major autoantigen in autoimmune thyroid disease (AITD). It is believed that the majority of TPO autoantibodies bind to an immunodominant region consisting of two overlapping domains. Precise location of these domains would help our understanding of the interaction between TPO and TPO autoantibodies. 4F5 is a mouse monoclonal antibody (IgG1, kappa) that reacts with high affinity (2.6 x 10(10) mol/L(-1)) with one of the major autoantigenic regions on TPO. Heavy chain genes of 4F5 were from the VH1 germline gene family, germline genes for the D region could not be assigned and the J region was from the JH2 germline. Light chain genes were from Vkappa4/5 and Jkappa2, germline gene families. The Fab fragment of 4F5 was prepared by papain digestion, purified, crystallized, and the structure solved to 1.9 A using molecular replacement. The refined structure had an R factor of 19.5% and a free R factor of 23.9%. Deduced amino acid sequence and amino acid sequence obtained from diffraction analysis were compared and used to finalize the 4F5 Fab model. Structural analysis indicated that the structure of 4F5 is that of a standard Fab and its combining site is flat and is rich in tyrosine residues. Comparison of the structure of 4F5 with that of a TPO autoantibody Fab, TR1.9 suggests that the two antibodies are unlikely to recognise the same structures on TPO.