Published online 6 November 2000.
© The Rockefeller University Press, 0022-1007/2000/11/1223/ $5.00
The Journal of Experimental Medicine, Volume 192, Number 9, November 6, 2000 1223-1236
The Binding Site of Human Adenosine Deaminase for Cd26/Dipeptidyl Peptidase IV: The Arg142gln Mutation Impairs Binding to Cd26 but Does Not Cause Immune Deficiency
Eva Richarda,
Francisco X. Arredondo-Vegaa,
Ines Santistebana,
Susan J. Kellya,
Dhavalkumar D. Patela,b, and
Michael S. Hershfielda,c
a Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710
b Department of Immunology, Duke University Medical Center, Durham, North Carolina 27710
c Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710
Duke University Medical Center, Box 3049, Durham, NC 27710.919-684-4168919-684-4184
Human, but not murine, adenosine deaminase (ADA) forms a complex with the cell membrane protein CD26/dipeptidyl peptidase IV. CD26-bound ADA has been postulated to regulate extracellular adenosine levels and to modulate the costimulatory function of CD26 on T lymphocytes. Absence of ADA–CD26 binding has been implicated in causing severe combined immunodeficiency due to ADA deficiency. Using human–mouse ADA hybrids and ADA point mutants, we have localized the amino acids critical for CD26 binding to the helical segment 126–143. Arg142 in human ADA and Gln142 in mouse ADA largely determine the capacity to bind CD26. Recombinant human ADA bearing the R142Q mutation had normal catalytic activity per molecule, but markedly impaired binding to a CD26+ ADA-deficient human T cell line. Reduced CD26 binding was also found with ADA from red cells and T cells of a healthy individual whose only expressed ADA has the R142Q mutation. Conversely, ADA with the E217K active site mutation, the only ADA expressed by a severely immunodeficient patient, showed normal CD26 binding. These findings argue that ADA binding to CD26 is not essential for immune function in humans.
Key Words: adenosine deaminase deficiency severe combined immunodeficiency T lymphocyte protein–protein interaction adenosine deaminase complexing protein
Abbreviations used in this paper: ADA, adenosine deaminase; ADA-CP, ADA complexing protein; Ado, adenosine; dAdo, 2'-deoxyadenosine; DPPIV, dipeptidyl peptidase IV; FPLC, fast protein liquid chromatography.
© 2000 The Rockefeller University Press

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