The arbitrium system is employed by phages of the SPbeta family to communicate with their progeny during infection to decide either to follow the lytic or the lysogenic cycle. The system is controlled by a peptide, AimP, that binds to the regulator AimR, inhibiting its DNA-binding activity and expression of aimX. Although the structure of AimR has been elucidated for phages SPβ and phi3T, there is still controversy regarding the molecular mechanism of AimR function, with two different proposed models for SPβ. In this study, we deepen our understanding of the system by solving the structure of an additional AimR that shows chimerical characteristics with the SPβ receptor. The crystal structures of this AimR (apo, AimP-bound and DNA-bound) together with in vitro and in vivo analyses confirm a mechanism of action by AimP-induced conformational restriction, shedding light on peptide specificity and cross regulation with relevant biological implications.

SPbeta 家族的噬菌体利用仲裁系统在感染过程中与其后代进行通信，以决定遵循裂解循环或溶原循环。该系统由肽 AimP 控制，AimP 与调节剂 AimR 结合，抑制其 DNA 结合活性和target X 的表达。尽管噬菌体 SPβ 和 phi3T 的 AimR 结构已被阐明，但关于其分子结构仍存在争议。 AimR 功能的机制，有两种不同的 SPβ 模型。在这项研究中，我们通过解析另一个 AimR 的结构来加深对该系统的理解，该 AimR 显示出与 SPβ 受体的嵌合特征。该 AimR（apo、AimP 结合和 DNA 结合）的晶体结构以及体外和体内分析证实了 AimP 诱导的构象限制的作用机制，揭示了肽特异性和交叉调节以及相关的生物学意义。