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Structural features of CD4 required for binding to HIV.
C C Ibegbu1, M S Kennedy, P J Maddon
1Division of Host Factors, Centers for Disease Control, Atlanta, GA 30333.
Journal of Immunology (Baltimore, Md. : 1950)
|April 1, 1989
Summary
Soluble CD4 (sCD4) protein inhibits HIV binding to T cells. Its activity depends on disulfide bonds, but active fragments can be generated, requiring proper structure for HIV binding.
Area of Science:
- Immunology
- Virology
- Biochemistry
Background:
- The CD4 glycoprotein is the primary cellular receptor for human immunodeficiency virus (HIV).
- Soluble CD4 (sCD4) is a potential therapeutic agent to block HIV entry into CD4+ T cells.
Purpose of the Study:
- To investigate the structural requirements of sCD4 for inhibiting HIV binding.
- To identify functional domains within sCD4 responsible for HIV interaction.
Main Methods:
- sCD4 was subjected to various chemical (disulfide bond reduction, alkylation), enzymatic (proteolysis), and physical treatments.
- Inhibitory activity was assessed by measuring the capacity of treated sCD4 to block HIV binding to CD4+ T cells.
- HIV-binding fragments were identified using biochemical assays.
Main Results:
- Disulfide bond reduction in denaturing conditions abolished sCD4 inhibitory activity, while reduction in non-denaturing conditions had no effect.
- Carbohydrate modifications did not impact sCD4's capacity to inhibit HIV binding.
- Proteolytic digestion with trypsin or endoproteinase Glu-C destroyed activity, but limited digestion yielded active fragments, including a 23 kDa fragment that binds HIV.
Conclusions:
- Intrachain disulfide bonds are crucial for maintaining the tertiary structure and full inhibitory activity of sCD4.
- While sCD4 can be fragmented to retain HIV-binding capacity, proper structural conformation is essential for optimal affinity to HIV.