Molecular Recognition of Muramyl Dipeptide Occurs in the Leucine-rich Repeat Domain of Nod2

Genetic mutations in the innate immune
receptor nucleotide-binding oligomerization domain-containing 2 (Nod2)
have demonstrated increased susceptibility to Crohn’s disease,
an inflammatory bowel disease that is hypothesized to be accompanied
by changes in the gut microbiota. Nod2 responds to the presence of
bacteria, specifically a fragment of the bacterial cell wall, muramyl
dipeptide (MDP). The proposed site of this interaction is the leucine-rich
repeat (LRR) domain. Surface plasmon resonance and molecular modeling
were used to investigate the interaction of the LRR domain with MDP.
A functional and pure LRR domain was obtained from Escherichia coli expression in high yield. The LRR
domain binds to MDP with high affinity, with a KD of 212 ± 24 nM. Critical portions of the receptor were
determined by mutagenesis of putative binding residues. Fragment analysis
of MDP revealed that both the peptide and carbohydrate portion contribute
to the binding interaction.

先天免疫受体含核苷酸结合寡聚化结构域2（Nod2）的遗传突变，已被证实会增加克罗恩病的易感性——克罗恩病是一种炎症性肠病，现有假说认为其伴随肠道菌群的改变。Nod2可响应细菌的存在，具体识别细菌细胞壁的组分胞壁酰二肽（MDP）。二者相互作用的推定位点为富亮氨酸重复（LRR）结构域。本研究采用表面等离子体共振与分子建模技术，探究LRR结构域与MDP的相互作用。通过大肠杆菌表达体系，以高收率获得了功能完整且纯度优异的LRR结构域。该结构域与MDP具有高亲和力结合，解离常数（KD）为212 ± 24 nM。通过对推定结合残基进行诱变实验，确定了该受体的关键结合区域。对MDP的片段分析显示，其肽段与碳水化合物组分均对结合相互作用有所贡献。