Calreticulin Interacts with Newly Synthesized Human Immunodeficiency Virus Type 1 Envelope Glycoprotein, Suggesting a Chaperone Function Similar to That of Calnexin

doi:10.1074/jbc.271.1.97

Calreticulin Interacts with Newly Synthesized Human Immunodeficiency Virus Type 1 Envelope Glycoprotein, Suggesting a Chaperone Function Similar to That of Calnexin (*)

Ahlert Otteken(§) and
Bernard Moss(¶)

From the Laboratory of Viral Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892

^¶ To whom correspondence should be addressed. Tel.: 301-496-9869; Fax: 301-480-1147; bernard_moss{at}nih.gov.

Abstract

The ubiquitous eukaryotic protein calreticulin has been detected in a wide variety of different cell types. Recently, calreticulin was found to bind in vitro to a number of proteins isolated from the endoplasmic reticulum. In addition, calreticulin has sequence similarities with the molecular chaperone calnexin. These data suggest that calreticulin might also act as a chaperone. We found that calreticulin associated transiently with a large number of newly synthesized cellular proteins. In cells expressing recombinant human immunodeficiency virus (HIV) envelope glycoprotein, gp160 bound transiently to calreticulin with a peak at 10 min after its synthesis. Binding of gp120 to calreticulin was not detected because proteolytic cleavage of gp160 occurs in the trans-Golgi. Nonglycosylated HIV envelope protein was not associated with calreticulin, suggesting a requirement for N-linked oligosaccharides on newly synthesized proteins as has been reported for calnexin. The in vivo binding kinetics of calnexin and calreticulin to gp160 were very similar. Sequential immunoprecipitations provided evidence for the existence of ternary complexes of gp160, calreticulin, and calnexin. The data suggested that most of the gp160 associated with calreticulin was also bound to calnexin but that only a portion of the gp160 associated with calnexin was also bound to calreticulin.

Footnotes

↵^§ Supported by a fellowship from the German Bundesministerium für Forschung und Technologie, Stipendienprogramm Infektionskrankheiten.
↵* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

ER

endoplasmic reticulum

BiP

immunoglobulin heavy chain- binding protein

HIV

human immunodeficiency virus

HIV-1

HIV type 1

VSV

vesicular stomatitis virus

PAGE

polyacrylamide gel electrophoresis.
- Received August 2, 1995.
- Revision received October 21, 1995.