Expression of rat endopeptidase-24.18 in COS-1 cells: membrane topology and activity - PubMed (original) (raw)

Expression of rat endopeptidase-24.18 in COS-1 cells: membrane topology and activity

P E Milhiet et al. Biochem J. 1994.

Abstract

Endopeptidase-24.18 (E-24.18; EC 3.4.24.18) is a metallopeptidase of the astacin family and is highly expressed in kidney brush-border membranes of rodents. Rat E-24.18 consists of two disulphide-linked alpha/beta dimers [(alpha/beta)2]. In order to investigate the mechanisms of assembly and the importance of each subunit in the enzymic process, the cloned cDNAs for the rat alpha and beta subunits were transiently expressed either alone or together in COS-1 cells. Immunoblotting of cell extracts and spent culture media showed that, when expressed alone, the alpha subunit is secreted, whereas the beta subunit is membrane-bound. In alpha/beta-transfected cells, the alpha subunit remained membrane-bound, but could be released from the cell surface after papain treatment or after incubation with 10 mM dithiothreitol. Furthermore, mutants of the alpha subunit in which the putative C-terminal anchor domain was deleted could still form cell-associated alpha/beta dimers. These results are consistent with a topological model of E-24.18 in which the beta subunit is anchored in the plasma membrane and the alpha subunit is retained at the cell surface through disulphide bridge(s) with the beta subunit. Both the alpha and beta recombinant subunits expressed in COS-1 cells showed little azocasein-degrading activity. However, activity of either individual subunits of alpha/beta dimers was increased after mild trypsin digestion, suggesting that in COS-1 cells the enzymes are synthesized as zymogens. Finally, inactivation of the alpha subunit by site-directed mutagenesis of Glu-157, which is believed to play a role in catalysis, showed that both subunits participate in the enzymic activity of the heterodimer.

PubMed Disclaimer

Similar articles

Cited by

References

    1. Cell. 1981 Jan;23(1):175-82 - PubMed
    1. J Biol Chem. 1991 Mar 25;266(9):5540-6 - PubMed
    1. J Biol Chem. 1991 Sep 15;266(26):17350-7 - PubMed
    1. Arch Biochem Biophys. 1991 Nov 1;290(2):549-53 - PubMed
    1. Biochemistry. 1991 Oct 22;30(42):10065-74 - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources