Structural requirements of six naturally occurring isoforms of the IL-18 binding protein to inhibit IL-18
Structural requirements of six naturally occurring isoforms of the IL-18 binding protein to inhibit IL-18
复制标题
DOI：
10.1073/pnas.97.3.1190
复制
发表时间：
2000-02-01
影响因子：
11.1
通讯作者：
Dinarello, CA
中科院分区：
文献类型：
--
作者：
Kim, SH;Eisenstein, M;Dinarello, CA
一种新的、组成性表达和分泌的IL-18结合蛋白（IL-18BP）中和IL-18，从而抑制ifn - γ的产生，导致t辅助型1免疫反应减少。在本研究中，通过mRNA剪接和在不同cDNA文库中发现的四种人和两种小鼠同种异构体被表达、纯化并评估其结合和中和IL-18的生物活性。人IL-18BP异构体a （IL-18BPa）对IL-18的亲和力最大，其打开速率快，关闭速率慢，解离常数（K-d）为399 pM。IL-18BPc除29个c端氨基酸外，与IL-18BPa具有相同的Ig结构域；IL-18BPc的K-d （2.94 nM）降低了10倍。尽管如此，IL-18BPa和IL-18BPc在摩尔过量2时能中和95%的il - 18>。IL-18BPb和lL-18BPd异构体缺乏完整的Ig结构域，缺乏结合或中和IL-18的能力。小鼠IL-18BPc和IL-18BPd同种异构体具有相同的Ig结构域，也能在摩尔过量的情况下中和95%以上的小鼠IL-18。然而，小鼠IL-18BPd与人类IL-18BPa具有共同的c端基序，也能中和人类IL-18。分子建模发现IL-18BP的Ig结构域有一个大的静电和疏水混合结合位点，这可能是IL-18BP与配体高亲和力结合的原因。IL-18BP的功能性和非功能性亚型的优先分泌可能会影响免疫应答。
A novel, constitutively expressed and secreted IL-18 binding protein (IL-18BP) neutralizes IL-18 and thereby suppresses the production of IFN-gamma, resulting in reduced T-helper type 1 immune responses. In the present study, four human and two mouse isoforms, resulting from mRNA splicing and found in various cDNA libraries, were expressed, purified, and assessed for binding and neutralization of IL-18 biological activities. Human IL-18BP isoform a (IL-18BPa) exhibited the greatest affinity for IL-18 with a rapid on-rate, a slow off-rate, and a dissociation constant (K-d) Of 399 pM. IL-18BPc shares the Ig domain of IL-18BPa except for the 29 C-terminal amino acids; the K-d Of IL-18BPc is 10-fold less (2.94 nM). Nevertheless, IL-18BPa and IL-18BPc neutralize IL-18 >95% at a molar excess of two. IL-18BPb and lL-18BPd isoforms lack a complete Ig domain and lack the ability to bind or neutralize IL-18. Murine IL-18BPc and IL-18BPd isoforms, possessing the identical Ig domain, also neutralize >95% murine IL-18 at a molar excess of two. However, murine IL-18BPd, which shares a common C-terminal motif with human IL-18BPa, also neutralizes human IL-18. Molecular modeling identified a large mixed electrostatic and hydrophobic binding site in the Ig domain of IL-18BP, which could account for its high affinity binding to the ligand. It is likely that preferential secretion of functional and nonfunctional isoforms of IL-18BP affect the immune response.