X-ray structures of fragments from binding and nonbinding versions of a humanized anti-CD18 antibody: structural indications of the key role of VH residues 59 to 65.
X-ray crystal structures of fragments from two different humanized anti-CD18 antibodies are reported. The Fv fragment of the nonbinding version has been refined in space group C2 with a = 64.2 A, b = 61.3 A, c = 51.8 A, and beta = 99 degrees to an R-value of 18.0% at 1.9 A, and the Fab fragment of the tight-binding version has been refined in space group P3 with a = 101. A and c = 45.5 A to an R-value of 17.8% at 3.0 A resolution. The very large difference in their binding affinity (> 1000-fold) is attributed to large and local structural differences in the C-terminal part of CDR-H2, and from this we conclude there is direct contact between this region and antigen when they combine. X-ray structures of antibody-antigen complexes available in the literature have yet to show this part of CDR-H2 in contact with antigen, despite its hypervariable sequence. Implications of this result for antibody humanization are discussed.
Eigenbrot
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Department of Protein Engineering, Genentech, Inc., South San Francisco, California 94080-4990.
Gonzalez
T
T
Mayeda
J
J
Carter
P
P
Werther
W
W
Hotaling
T
T
Fox
J
J
Kessler
J
J
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000737:chemistry*; D015703:Antigens, CD / Q000276:immunology*; D001667:Binding, Competitive; D018821:CD18 Antigens; D018360:Crystallography, X-Ray; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry*; D007128:Immunoglobulin Fragments / Q000737:chemistry*; D007135:Immunoglobulin Variable Region / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry; D013601:T-Lymphocytes / Q000276:immunology
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D018821:CD18 Antigens; D007140:Immunoglobulin Fab Fragments; D007128:Immunoglobulin Fragments; D007135:Immunoglobulin Variable Region; D011994:Recombinant Proteins; C055966:immunoglobulin Fv