Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transmembrane disposition of the NH2-terminal third of the Na,K-ATPase alpha subunit was studied using an experimental approach that involved in vitro endoplasmic reticulum membrane insertion of chimeras. These chimeras consisted of four truncated amino-terminal segments of the alpha subunit linked at amino acid residues 126, 179, 313, and 439 to chloramphenicol acetyltransferase (CAT), a reporter protein, that contains a consensus sequence for N-linked glycosylation. The fusion sites were located after one of the four hydrophobic segments (H1-H4). The results showed that the chimeras in which the alpha subunit was truncated at positions 126 and 313 were glycosylated, and the glycosylated peptides were protected by membranes from proteolysis. However, the other two chimeras were not glycosylated and the inserted peptides were digested by protease into fragments which did not immunoprecipitate with anti-CAT. These results clearly demonstrate that hydrophobic segments H1 and H3 function as signal/anchor type II, and H2 and H4 function as halt transfer signals. Furthermore, membrane insertion of the NH2-terminal third of Na,K-ATPase alpha subunit is achieved by a series of alternate signal/anchor type II and halt transfer sequences.
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PMID:Four hydrophobic segments in the NH2-terminal third (H1-H4) of Na,K-ATPase alpha subunit alternately initiate and halt membrane translocation of the newly synthesized polypeptide. 774 48

We studied the topogenic properties of five hydrophobic segments (H5-H9) in the COOH-terminal third of Na,K-ATPase alpha subunit using in vitro insertion of fusion proteins into endoplasmic reticulum membranes. These fusion proteins consisted of several different lengths of truncated alpha subunit starting at Met729 and a reporter protein, chloramphenicol acetyltransferase, that was linked in frame after each hydrophobic segment. We found that membrane insertion of the newly synthesized COOH-terminal third was initiated by H5 and terminated by H9, indicating that here only H5 and H9 have topogenic function. The other three, H6-H8, did not have topogenic function in the native context and were translocated into the endoplasmic reticulum lumen. These results were in striking contrast to the previous models in which four or six hydrophobic segments were proposed to cross the membrane. Furthermore, the findings suggest a novel mechanism for achieving the final membrane topology of the COOH-terminal third of the alpha subunit.
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PMID:Only the first and the last hydrophobic segments in the COOH-terminal third of Na,K-ATPase alpha subunit initiate and halt, respectively, membrane translocation of the newly synthesized polypeptide. Implications for the membrane topology. 857 22