Open AccessA tetrameric complex of membrane proteins in the endoplasmic reticulum
Author(s) -
HARTMANN Enno,
GÖRLICH Dirk,
KOSTKA Susanne,
OTTO Albrecht,
KRAFT Regine,
KNESPEL Signe,
BÜRGER Elke,
RAPOPORT Tom A.,
PREHN Siegfried
Publication year - 1993
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1993.tb17933.x
Subject(s) - translocon , endoplasmic reticulum , protein subunit , signal peptide , stim1 , membrane , biochemistry , biology , gamma subunit , membrane protein , peptide sequence , microbiology and biotechnology , chemistry , biophysics , gene
The translocation site (translocon), at which nascent polypeptides pass through the endoplasmic reticulum membrane, contains a component previously called ‘signal sequence receptor’ that is now renamed as ‘translocon‐associated protein’ (TRAP). Two glycosylated subunits of the TRAP complex have been identified before (α and β subunits). We now show that the TRAP complex is actually comprised of four membrane proteins (α, β, γ, δ), present in a stoichiometric relation, which are genuine neighbours in intact microsomes. The amino acid sequences of the additional, non‐glycosylated subunits were deduced from cloning of the corresponding cDNAs. The δ subunit spans the membrane only once and has its major portion, containing a disulfide bridge, at the lumenal side. The γ subunit is predicted to span the membrane four times.