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PDBsum entry 3d9a
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Hydrolase/immune system
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PDB id
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3d9a
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Contents |
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129 a.a.
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213 a.a.
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210 a.a.
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References listed in PDB file
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Key reference
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Title
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Light chain somatic mutations change thermodynamics of binding and water coordination in the hyhel-10 family of antibodies.
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Authors
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M.Acchione,
C.A.Lipschultz,
M.E.Desantis,
A.Shanmuganathan,
M.Li,
A.Wlodawer,
S.Tarasov,
S.J.Smith-Gill.
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Ref.
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Mol Immunol, 2009,
47,
457-464.
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PubMed id
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Abstract
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Thermodynamic and structural studies addressed the increased affinity due to
L-chain somatic mutations in the HyHEL-10 family of affinity matured IgG
antibodies, using ITC, SPR with van't Hoff analysis, and X-ray crystallography.
When compared to the parental antibody H26L26, the H26L10 and H26L8 chimeras
binding to lysozyme showed an increase in favorable DeltaG(o) of -1.2+/-0.1 kcal
mol(-1) and -1.3+/-0.1 kcal mol(-1), respectively. Increase in affinity of the
H26L10 chimera was due to a net increase in favorable enthalpy change with
little difference in change in entropy compared to H26L26. The H26L8 chimera
exhibited the greatest increase in favorable enthalpy but also showed an
increase in unfavorable entropy change, with the result being that the
affinities of both chimeras were essentially equivalent. Site-directed L-chain
mutants identified the shared somatic mutation S30G as the dominant contributor
to increasing affinity to lysozyme. This mutation was not influenced by H-chain
somatic mutations. Residue 30L is at the periphery of the binding interface and
S30G effects an increase in hydrophobicity and decrease in H-bonding ability and
size, but does not make any new energetically important antigen contacts. A new
1.2-A structure of the H10L10-HEL complex showed changes in the pattern of both
inter- and intra-molecular water bridging with no other significant structural
alterations near the binding interface compared to the H26L26-HEL complex. These
results highlight the necessity for investigating both the structure and the
thermodynamics associated with introduced mutations, in order to better assess
and understand their impact on binding. Furthermore, it provides an important
example of how backbone flexibility and water-bridging may favorably influence
the thermodynamics of an antibody-antigen interaction.
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