The signal sequence receptor has a second subunit and is part of a translocation complex in the endoplasmic reticulum as probed by bifunctional reagents

D. Gorlich, S. Prehn, E. Hartmann, J. Herz, A. Otto, R. Kraft, M. Wiedmann, S. Knespel, B. Dobberstein, T. A. Rapoport

51 Zitate (Scopus)

Abstract

Bifunctional cross-linking reagents were used to probe the protein environment in the ER membrane of the signal sequence receptor (SSR), a 34-kD integral membrane glycoprotein (Wiedmann, M., T.V. Kurzchalia, F. Hartmann, and T.A. Rapoport. 1987. Nature [Lond.]. 328:830-833). The proximity of several polypeptides was demonstrated. A 22-kD glycoprotein was identified tightly bound to the 34-kD SSR even after membrane solubilization. The 34-kD polypeptide, now termed αSSR, and the 22-kD polypeptide, the βSSR, represent a heterodimer. We report on the sequence of the βSSR, its membrane topology, and on the mechanism of its integration into the membrane. Cross-linking also produced dimers of the α-subunit of the SSR indicating that oligomers of the SSR exist in the ER membrane. Various bifunctional cross-linking reagents were used to study the relation to ER membrane proteins of nascent chains of preprolactin and β-lactamase at different stages of their translocation through the membrane. The predominant cross-linked products obtained in high yields contained the αSSR, indicating in conjunction with previous results that it is a major membrane protein in the neighborhood of translocating nascent chains of secretory proteins. The results support the existence of a translocon, a translocation complex involving the SSR, which constitutes the specific site of protein translocation across the FR membrane.

OriginalspracheEnglisch
ZeitschriftJournal of Cell Biology
Jahrgang111
Ausgabenummer6 I
Seiten (von - bis)2283-2294
Seitenumfang12
ISSN0021-9525
DOIs
PublikationsstatusVeröffentlicht - 01.12.1990

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