Correlation of structures and functions of the semaphorin/neuropilin interaction

3类信号素被Furin蛋白水解性切割，导致生物活性的复杂调节。一些3类信号素与细胞表面辅助受体Nrp1结合，这是与细胞高亲和力结合所必需的。许多已知的Nrp1结合肽含有(R/K)XXR序列，该序列与Furin的识别基序相同。Sema3A在其基本结构域中有七个(R/K)XXR序列。然而，对实际切割位点的鉴定以及对关键Nrp1结合序列的精细定位一直是不可能的。通过有无呋喃抑制剂的综合诱变和MS分析，确定了Sema3A碱性结构域中主要的Nrp1结合部位。暴露这个部位需要在生物合成过程中用呋喃处理，但它被额外的上游裂解的细胞蛋白水解酶去除，导致失活。这些信息被用来设计具有结构性活性和抵抗失活的突变体。

Class-3 semaphorins are proteolytically cleaved by furin, resulting in a complex modulation of biological activity. Some class-3 semaphorins bind to cell surface coreceptor Nrp1, which is necessary for high affinity binding to the cells. Many known Nrp1-binding peptides contain (R/K)XXR sequence which is same as a recognition motif for furin. Sema3A has seven (R/K)XXR sequences in its basic domain. However, identification of the actual cleavage sites as well as the fine mapping of the critical Nrp1 binding sequence has not been possible. Through comprehensive mutagenesis and MS-analysis in the presence or absence of the furin inhibitor, major Nrp1 binding site within the Sema3A basic domain was identified. Exposure of this site requires processing by furin during the biosynthesis, but it is removed by additional upstream cleavages by cellular proteases, resulting in the inactivation. This information was used to design mutant that is constitutively active and resistant to inactivation.