|Detection of Human Cathepsin H by Western Blot. Western blot shows lysates of HepG2 human hepatocellular carcinoma cell line, A431 human epithelial carcinoma cell line, human kidney tissue, and human lung tissue. PVDF membrane was probed with 0.2 µg/mL of Sheep Anti-Human Cathepsin H Antigen Affinity-purified Polyclonal Antibody (Catalog # AF7516) followed by HRP-conjugated Anti-Sheep IgG Secondary Antibody (Catalog # HAF016). A specific band was detected for Cathepsin H at approximately 28 kDa (as indicated). This experiment was conducted under reducing conditions and using Immunoblot Buffer Group 1.|
Cathepsin H (CTSH; alos CPSB) is a 28-30 kDa ubiquitously expressed member of the peptidase C1 family of cysteine lysosomal enzymes. Depending upon the isoform, it may either be secreted or retained in the lysosomes. Although this family of enzymes plays a key role in general intracellular molecule degradation, CTSH is also known to participate in other activities. Such activities include the activation of progranzyme B, the late stage processing of pulmonary surfactant protein B, and the cleavage, in endosomes, of TLR3, allowing for subsequent TLR signaling. Human preproCTSH is 335 amino acids (aa) in length. It contains one 22 aa signal peptide, a 75 aa prosequence (aa 23-97), an intervening "mini fragment" (aa 98-105), a second prosequence (aa 106-115), and a 220 aa C-terminal mature region that could be further cleaved after Asn292 into two peptide fragments. CTSH is self-activating. The 40-42 kDa proprecursor (aa 23-335) is cleaved thrice to initially generate a 30 kDa intermediate form, followed by a 28 kDa mature form that is covalently attached to the aforementioned "mini fragment". Further processing at the C-terminus may create a smaller 24-25 kDa mature segment. CTSH is unusual in that it possess both aminopeptidase and endopeptidase activity. While endopeptidase activity is intrinsic to the mature region, aminopeptidase activity requires the presence of a covalently-linked "mini fragment". There is one splice variant that shows a deletion of aa 11-22. Although this occurs within the signal sequence, the molecule is secreted and shows high enzymatic activity. Over aa 23-335, human CTSH shares 84% aa sequence identity with mouse CTSH.
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