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Journal of Virology, April 1999, p. 3169-3175, Vol. 73, No. 4
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Amphotropic Murine Leukemia Virus Entry Is Determined by Specific Combinations of Residues from Receptor Loops 2 and 4

Mikkel D. Lundorf,1 Finn S. Pedersen,1,2 Bryan O'Hara,3 and Lene Pedersen1,*

Department of Molecular and Structural Biology1 and Department of Medical Microbiology and Immunology,2 University of Aarhus, DK-8000 Aarhus C, Denmark, and Department of Molecular Biology, Wyeth-Ayerst Research, Pearl River, New York 109653

Received 28 August 1998/Accepted 3 January 1999

Pit2 is the human receptor for amphotropic murine leukemia virus (A-MuLV); the related human protein Pit1 does not support A-MuLV entry. Interestingly, chimeric proteins in which either the N-terminal or the C-terminal part of Pit2 was replaced by the Pit1 sequence all retained A-MuLV receptor function. A possible interpretation of these observations is that Pit1 harbors sequences which can specify A-MuLV receptor function when presented in a protein context other than Pit1, e.g., in Pit1-Pit2 hybrids. We reasoned that such Pit1 sequences might be identified if presented in the Neurospora crassa protein Pho-4. This protein is distantly related to Pit1 and Pit2, predicted to have a similar membrane topology with five extracellular loops, and does not support A-MuLV entry. We show here that introduction of the Pit1-specific loop 2 sequence conferred A-MuLV receptor function upon Pho-4. Therefore, we conclude that (i) a functional A-MuLV receptor can be constructed by combining sequences from two proteins each lacking A-MuLV receptor function and that (ii) a Pit1 sequence can specify A-MuLV receptor function when presented in another protein context than that provided by Pit1 itself. Previous results indicated a role of loop 4 residues in A-MuLV entry, and the presence of a Pit2-specific loop 4 sequence was found here to confer A-MuLV receptor function upon Pho-4. Moreover, the introduction of a Pit1-specific loop 4 sequence, but not of a Pit2-specific loop 4 sequence, abolished the A-MuLV receptor function of a Pho-4 chimera harboring the Pit1-specific loop 2 sequence. Together, these data suggest that residues in both loop 2 and loop 4 play a role in A-MuLV receptor function. A-MuLV is, however, not dependent on the specific Pit2 loop 2 and Pit2 loop 4 sequences for entry; rather, the role played by loops 2 and 4 in A-MuLV entry can be fulfilled by several different combinations of loop 2 and loop 4 sequences. We predict that the residues in loops 2 and 4, identified in this study as specifying A-MuLV receptor function, are to be found among those not conserved among Pho-4, Pit1, and Pit2.

* Corresponding author. Mailing address: Department of Molecular and Structural Biology, University of Aarhus, C. F. Møllers Allé, Bldg. 130, DK-8000 Aarhus C, Denmark. Phone: 45-8942-2633. Fax: 45-8619-6500. E-mail: LP{at}mbio.aau.dk.

Journal of Virology, April 1999, p. 3169-3175, Vol. 73, No. 4
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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