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Sequence and Expression of a Membrane-Associated C-Type Lectin that Exhibits CD4-Independent Binding of Human Immunodeficiency Virus Envelope Glycoprotein gp120
Benson M. Curtis, Sonya Scharnowski and Andrew J. Watson
Proceedings of the National Academy of Sciences of the United States of America
Vol. 89, No. 17 (Sep. 1, 1992), pp. 8356-8360
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/2361356
Page Count: 5
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The binding of the human immunodeficiency virus (HIV) envelope glycoprotein gp120 to the cell surface receptor CD4 has been considered a primary determinant of viral tropism. A number of cell types, however, can be infected by the virus, or bind gp120, in the absence of CD4 expression. Human placenta was identified as a tissue that binds gp120 in a CD4-independent manner. A placental cDNA library was screened by expression cloning and a cDNA (clone 11) encoding a gp120-binding protein unrelated to CD4 was isolated. The 1.3-kilobase cDNA predicts a protein of 404 amino acids with a calculated Mr of 45,775 and organized into three domains: an N-terminal cytoplasmic and hydrophobic region, a set of seven complete and one incomplete tandem repeat, and a C-terminal domain with homology to C-type (calcium-dependent) lectins. A type II membrane orientation (N-terminal cytoplasmic) is predicted both by the cDNA sequence and by the reactivity of C-terminal peptide-specific antiserum with the surface of clone 11 transfected cells. Native and recombinant gp120 and whole virus bind transfected cells. gp120 binding is high affinity (Kd, 1.3-1.6 nM) and inhibited by mannan, D-mannose, and L-fucose; once bound, gp120 is internalized rapidly. Collectively, these data demonstrate that the gp120-binding protein is a membrane-associated mannose-binding lectin. Proteins of this type may play an important role in the CD4-independent association of HIV with cells.
Proceedings of the National Academy of Sciences of the United States of America © 1992 National Academy of Sciences