Residue Trp-48 of Tva is critical for viral entry but not for high-affinity binding to the SU glycoprotein of subgroup A avian leukosis and sarcoma viruses.

Abstract

Previously, mutant Tva receptors were classified as either partially or completely defective in mediating subgroup A avian leukosis and sarcoma virus (ALSV-A) entry (C. Bélanger, K. Zingler, and J. A. T. Young, J. Virol. 69:1019-1024, 1995; K. Zingler, C. Bélanger, R. Peters, D. Agard, and J. A. T. Young, J. Virol. 69:4261-4266, 1995). To specifically test the abilities of these mutant Tva proteins to bind ALSV-A surface (SU) protein, binding studies were performed with a subgroup A SU-immunoadhesin. This fusion protein is composed of the subgroup A Schmidt-Ruppin SU protein fused in frame to a rabbit immunoglobulin constant region. This reagent was conjugated to fluorescein isothiocyanate and used for flow cytometric analysis with transfected human 293 cells expressing different forms of Tva. The SU-immunoadhesin bound the wild-type Tva protein with a KD of approximately 1.5 nM. Amino acid substitutions that reduced viral entry at Asp-46 and at Cys-35 and Cys-50, which are predicted to form an intrachain disulfide bond in Tva, drastically reduced the binding affinity for the SU-immunoadhesin. Thus, the effects on viral entry of some mutations could be explained solely by changes in the binding affinity for ALSV-A SU. However, this was not true for other mutations tested, especially those with amino acid substitutions that replaced Trp-48. Compared with the wild-type receptor, these latter mutations led to approximately 43- to 200-fold reductions in viral infectivity but only to approximately 2.5- to 3.4-fold reductions in the binding affinity for the SU-immunoadhesin. These results support a role for Trp-48 of Tva in mediating steps of viral entry subsequent to binding ALSV-A SU.

• Authors: K Zingler, J A Young
• Journal: Journal of virology (J Virol) Vol. 70 Issue 11 Pg. 7510-6 (Nov 1996) ISSN: 0022-538X [Print] United States
• PMID: 8892869 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Avian Proteins
• Glycoproteins
• Receptors, Virus
• Tva receptor
• Viral Envelope Proteins
• Trypsin

Topics

• Animals
• Avian Leukosis Virus (metabolism)
• Avian Proteins
• Avian Sarcoma Viruses (metabolism)
• Binding Sites
• Cell Line, Transformed
• Cloning, Molecular
• Glycoproteins (genetics, metabolism)
• Humans
• Receptors, Virus (genetics, metabolism)
• Trypsin
• Viral Envelope Proteins (genetics, metabolism)