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[Primary structure of human protein pS2]
M C Rio1, P Lepage, P Diemunsch
1Laboratoire de Génétique moléculaire des Eucaryotes du C.N.R.S., Strasbourg.
Abstract:
We have previously reported that pS2 mRNA expressed in cultured epithelial cells derived from a hormone-dependent breast carcinoma (MCF-7 cells) is also expressed in mucosa cells of normal human stomach. This mRNA encodes a putative 84 amino-acid-long protein, which is secreted by both cell types after elimination of a signal peptide. We report here the purification of the pS2 protein, its trypsin digestion and amino-acid sequencing. The MCF-7 cell-secreted protein is 60 amino-acid-long and its sequence is in complete agreement with that deduced from the mRNA sequence. The presence of an N-terminal glutamic acid indicates that the signal peptidase releases a 24 amino-acid-long signal peptide. Analysis of tryptic peptides derived from the secreted gastric pS2 protein indicates that the signal peptide and the sequence of the first 48 amino-acids are identical to those of secreted MCF-7 pS2 protein, although the N-terminal amino-acid of the gastric protein may be cyclized as a pyroglumatic acid.
Insights
Researchers purified and sequenced the pS2 protein from both breast cancer cells (MCF-7) and normal stomach mucosa. The pS2 protein sequences were identical, confirming gene expression in distinct human tissues.
Area of Science:
- Molecular Biology
- Protein Chemistry
- Gastroenterology
Background:
- pS2 mRNA is expressed in hormone-dependent breast carcinoma cells (MCF-7) and normal human stomach mucosa.
- The mRNA encodes a putative 84 amino-acid protein secreted after signal peptide removal.
Purpose of the Study:
- To purify and characterize the pS2 protein secreted by MCF-7 cells and normal gastric mucosa.
- To confirm the identity and sequence of the pS2 protein in both cell types.
Main Methods:
- Purification of the pS2 protein from cell secretions.
- Trypsin digestion of the purified pS2 protein.
- Amino-acid sequencing of the resulting peptides.
Main Results:
- The secreted pS2 protein from MCF-7 cells is 60 amino acids long, matching the mRNA sequence.
- The N-terminal glutamic acid indicates a 24 amino-acid signal peptide.
- Gastric pS2 protein shares identical signal peptide and initial 48 amino acids with MCF-7 pS2 protein, with potential N-terminal pyroglutamic acid cyclization.
Conclusions:
- The pS2 protein sequence is conserved between breast cancer cells and normal gastric mucosa.
- Confirms the expression and secretion of a structurally identical pS2 protein in distinct human tissues.