Correlation of structures and functions of the semaphorin/neuropilin interaction

3类信号蛋白被弗林蛋白酶蛋白水解切割，导致生物活性的复杂调节。一些3类信号蛋白结合细胞表面辅助受体Nrp 1，这是高亲和力结合细胞所必需的。许多已知的Nrp 1结合肽含有（R/K）XXR序列，该序列与弗林蛋白酶的识别基序相同。Sema 3A在其基本结构域中有7个（R/K）XXR序列。然而，识别的实际切割位点以及精细映射的关键Nrp 1结合序列一直是不可能的。通过全面的诱变和MS分析，在存在或不存在的弗林蛋白酶抑制剂，主要Nrp 1结合位点内的Sema 3A基本结构域进行了鉴定。该位点的暴露需要在生物合成过程中被弗林蛋白酶处理，但它被细胞蛋白酶的额外上游切割去除，导致失活。该信息用于设计组成型活性和抗失活的突变体。

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.