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J. Virol., 05 1995, 2745-2750, Vol 69, No. 5
HB Bernstein, SP Tucker, SR Kar, SA McPherson, DT McPherson, JW Dubay, J Lebowitz, RW Compans and E Hunter
The transmembrane protein of human immunodeficiency virus type 1 (HIV- 1)
contains a leucine zipper-like (hydrophobic heptad) repeat which has been
predicted to form an amphipathic alpha helix. To evaluate the potential of
the hydrophobic heptad repeat to induce protein oligomerization, this
region of gp41 has been cloned into the bacterial expression vector pRIT2T.
The resulting plasmid, pRIT3, expresses a fusion protein consisting of the
Fc binding domain of monomeric protein A, a bacterial protein, and amino
acids 538 to 593 of HIV-1 gp41. Gel filtration chromatography demonstrated
the presence of oligomeric forms of the fusion protein, and analytical
centrifugation studies confirmed that the chimeric protein formed a
higher-order multimer that was greater than a dimer. Thus, we have
identified a region of HIV-1 gp41 which is capable of directing the
oligomerization of a fusion protein containing monomeric protein A. Point
mutations, previously shown to inhibit the biological activity of the HIV-1
envelope glycoprotein, have been engineered into the segment of gp41
contained in the fusion protein, and expressed mutant proteins were
purified and analyzed via fast protein liquid chromatography. A point
mutation in the heptad repeat, which changed the central isoleucine to an
alanine, caused a significant (> 60%) decrease in oligomerization,
whereas changing the central isoleucine to aspartate or proline resulted in
almost a complete loss of oligomerization. Deletions of one, two, or three
amino acids following the first isoleucine also resulted in a profound
decrease in oligomerization. The inhibitory effects of the mutations on
oligomer formation correlated with the effects of the same mutations on
envelope glycoprotein-mediated fusion. A possible role of the leucine
zipper-like region in the fusion process and in an oligomerization event
distinct from assembly of the envelope glycoprotein complex is discussed.
Copyright © 1995, American Society for Microbiology
Oligomerization of the hydrophobic heptad repeat of gp41
Department of Microbiology, University of Alabama at Birmingham 35294- 2170, USA.
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