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J. Virol., 03 1995, 1621-1627, Vol 69, No. 3
M Mulvey and DT Brown
Sindbis virus codes for two membrane glycoproteins, E1 and PE2, which
assemble into heterodimers within the endoplasmic reticulum. We have
examined the role of the molecular chaperone BiP (grp78) in the maturation
of these two proteins. E1, which folds into its mature conformation via at
least three intermediates differing in the configurations of their
disulfide bonds, was found to interact strongly and transiently with BiP
after synthesis. ATP depletion mediated by carbonyl cyanide
m-chlorophenylhydrazone treatment results in the stabilization of complexes
between BiP and E1. The depletion of intracellular ATP levels also greatly
inhibits conversions between the E1 folding intermediates and results in
the slow incorporation of E1 into disulfide-stabilized aggregates. These
results suggest that the ATP-regulated binding and release of BiP have a
role in modulating disulfide bond formation during E1 folding. In
comparison with E1, very little PE2 is normally recovered in association
with BiP. However, under conditions in which E1 folding is aberrant,
increased amounts of PE2 become directly associated with BiP. The formation
of these BiP-PE2 interactions occurs after E1 begins to misfold or fails to
fold efficiently. We propose that nascent PE2 is stable prior to pairing
with E1 for only a limited period of time, after which unpaired PE2 becomes
recognized by BiP. This implies that the productive association of PE2 and
E1 must occur within a restricted time frame and only after E1 has
accomplished certain folding steps mediated by BiP binding and release.
Kinetic studies which show that the pairing of E1 with PE2 is delayed after
translocation support this conclusion.
Copyright © 1995, American Society for Microbiology
Involvement of the molecular chaperone BiP in maturation of Sindbis virus envelope glycoproteins
Cell Research Institute, University of Texas at Austin 78713-7640.
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