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PubMed1994

Human placental calreticulin: purification, characterization and association with other proteins.

Calreticulin is an intracellular protein known to be involved in calcium binding, but is also known to appear as an autoantigen in certain autoimmune diseases. The cDNA sequence is known but the protein has not yet been well characterized at the amino acid level. Owing to the possible involvement of this protein in autoimmune disease and with the aim of making monoclonal antibodies for use in assay development and immunohistochemistry, we have purified calreticulin using human placental material. Amino acid analysis of the purified protein confirmed the cDNA-derived composition, and only one discrepancy between the cDNA-predicted sequence and the amino acid sequence was found by peptide mapping and microsequencing. The protein contains one disulfide bridge and has one free SH group and the protein is neither glycosylated nor phosphorylated. Affinity chromatography of a placental protein extract on a column with immobilized calreticulin showed the existence of at least six proteins interacting with calreticulin. Using the purified calreticulin in Western blots, two out of eight patients with autoimmune disease diagnosed as having anti DNA antibodies in their serum were found also to contain autoantibodies to calreticulin in their serum.

Amino Acid Sequence↗
PubMed2000

TRH-like peptides in prostate gland and other tissues.

This minireview is aimed to recapitulate the occurrence of TRH-like peptides in the prostate gland and other tissues and to discuss their known functions in the organism. The hypothalamic thyrotropin-releasing hormone (TRH) was the first chemically defined hypophyseotropic hormone with the primary structure pGLU-HIS-PRO.NH2. However, the presence of extrahypothalamic TRH-immunoreactive peptides was reported in peripheral tissues including the gastrointestinal tract, placenta, neural tissues, male reproductive system and certain endocrine tissues. It was supposed that this TRH immunoreactivity can partially originate from TRH-homologous peptides and that these peptides have significant cross-reactions with the antibody specific against authentic TRH. This assumption was confirmed by the identification of prostatic TRH immunoreactivity as pyroGLU-GLU-PRO.NH2 using fast atom bombardment mass spectrometry and gas phase sequence analysis. TRH-like peptides are characterized by substitution of the basic amino acid histidine (related to authentic TRH) for neutral or acidic amino acids, such as glutamic acid, phenylalanine, glutamine or tyrosine. The physiological role of TRH-like peptides in peripheral tissues is not precisely known, but they possess a C-terminal amide group which is characteristic for many biologically active peptides. The occurrence of these peptides in the male reproductive system can influence male fertility. They are also closely related to circulating thyroid and steroid hormones. There might be an important connection of TRH-like peptides to the prostatic local autocrine/paracrine network mediated by extrahypothalamic TRH immunoreactivity corresponding to TRH-like peptides and extrapituitary thyrotropin (TSH) immunoreactivity also found in the prostatic tissue. A similar system of intraepithelial lymphocyte hormonal regulation due to the local paracrine network of TRH/TSH has been described in the gastrointestinal tract. The local network of TRH-like peptides/TSH may be involved in possible regulation of prostatic growth.

Animals↗