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首页> 外文期刊>Journal of Molecular Biology >Tyrosine plays a dominant functional role in the paratope of a synthetic antibody derived from a four amino acid code.
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Tyrosine plays a dominant functional role in the paratope of a synthetic antibody derived from a four amino acid code.

机译：酪氨酸在衍生自四个氨基酸密码的合成抗体的互补位中起主要功能作用。

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摘要

The antigen-binding fragment Fab-YADS2 recognizes vascular endothelial growth factor (VEGF) and was derived from a library with chemical diversity restricted to only four amino acids (Tyr, Ser, Ala and Asp). The structure of the Fab:antigen complex revealed that the structural paratope is dominated by Tyr side-chains. Isothermal titration calorimetry and cell-based assays show that restricted chemical diversity does not limit the affinity or specificity of Fab-YADS2, which behaves in a manner comparable to natural antibodies. Mutagenesis experiments reveal that the functional paratope is dominated by Tyr, which represents 11 of the 15 functionally important residues. However, mutagenesis experiments also indicate that substitution of any of these tyrosine residues by Phe does not significantly affect binding to VEGF. Furthermore, saturation mutagenesis shows that replacement of three functionally important tyrosine residues by combinations of other hydrophobic residues is not only tolerated, but can actually improve affinity. The results support a model for naive antigen recognition in which large Tyr side-chains establish binding contacts with antigen, and small Ser and Ala side-chains serve as auxiliaries that help to position Tyr in favorable binding conformations. While Tyr may not be optimal for any particular antigen contact, it is nonetheless capable of mediating favorable interactions with a diverse array of surfaces. Furthermore, the side-chain hydroxyl group makes Tyr significantly more hydrophilic than Phe and other hydrophobic amino acids. Increased hydrophilicity may reduce non-specific binding in the unbound state, and this may be critical for a naive repertoire that is exposed to a diverse range of potential antigenic surfaces. The results show that the chemical nature of Tyr endows the amino acid with a privileged role in antigen recognition, and this likely explains the high abundance of Tyr in natural antigen-binding sites.
机译：抗原结合片段Fab-YADS2识别血管内皮生长因子（VEGF），并衍生自化学多样性仅限于四个氨基酸（Tyr，Ser，Ala和Asp）的文库。 Fab：抗原复合物的结构表明，结构互补位由Tyr侧链控制。等温滴定热法和基于细胞的测定法表明，受限制的化学多样性不会限制Fab-YADS2的亲和力或特异性，而Fab-YADS2的行为方式可与天然抗体媲美。诱变实验表明，功能性互补位以Tyr为主，它代表15个功能重要残基中的11个。但是，诱变实验还表明，这些酪氨酸残基被Phe取代不会显着影响与VEGF的结合。此外，饱和诱变表明用其他疏水残基的组合代替三个功能重要的酪氨酸残基不仅可以耐受，而且实际上可以提高亲和力。结果支持天真抗原识别的模型，其中大Tyr侧链建立了与抗原的结合接触，而小Ser和Ala侧链充当了辅助剂，有助于将Tyr定位在有利的结合构象中。尽管Tyr对于任何特定的抗原接触可能都不是最佳选择，但它仍能够介导与各种表面的良好相互作用。此外，侧链羟基使Tyr的亲水性明显高于Phe和其他疏水性氨基酸。增加的亲水性可能会减少未结合状态下的非特异性结合，这对于暴露于各种潜在抗原表面的幼稚库可能至关重要。结果表明，Tyr的化学性质赋予氨基酸在抗原识别中的特权，这可能解释了Tyr在天然抗原结合位点中的丰度很高。

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