Department of Biochemistry, Bose Institute, P-1/12, C.I.T. Scheme VIIM, Kolkata, India.
Arch Biochem Biophys. 2010 Jan 15;493(2):175-83. doi: 10.1016/j.abb.2009.10.010. Epub 2009 Oct 22.
The CII protein of bacteriophage lambda is the key regulator for the lytic-lysogenic choice of the viral lifecycle. An unstable homotetrameric transcription activator of the three phage promoters p(E), p(I) and p(aQ), lambdaCII is stabilized by lambdaCIII and destabilized by the host protease, Escherichia coli HflB (FtsH). In addition, other E. coli proteins HflK, HflC and HflD also influence lysogeny by acting upon CII. Among these, HflD (22.9kDa), a peripheral membrane protein that is exposed towards the cytoplasm, interacts with CII and decreases the frequency of lysogenization of lambda by stimulating the degradation of CII. In this study, we show that in addition to helping CII degradation, HflD inhibits the DNA binding by CII, thereby inhibiting CII-dependent transcription activation. From biochemical, biophysical and modelling studies we also suggest that HflD-CII interaction takes place through the Cys31-accessible surface area of monomeric HflD, which binds to tetrameric CII as a 1:1 complex.
噬菌体 lambda 的 CII 蛋白是病毒生命周期裂解-溶源选择的关键调节剂。CII 是三个噬菌体启动子 p(E)、p(I)和 p(aQ)的不稳定四聚体转录激活因子，由 lambdaCIII 稳定，由宿主蛋白酶大肠杆菌 HflB（FtsH）不稳定。此外，其他大肠杆菌蛋白 HflK、HflC 和 HflD 也通过作用于 CII 影响溶原性。其中，HflD（22.9kDa）是一种朝向细胞质暴露的外周膜蛋白，与 CII 相互作用并通过刺激 CII 的降解来降低 lambda 的溶原率。在这项研究中，我们表明，除了帮助 CII 降解外，HflD 还抑制 CII 的 DNA 结合，从而抑制 CII 依赖性转录激活。从生化、生物物理和建模研究中，我们还提出 HflD-CII 相互作用发生在单体 HflD 的 Cys31 可及表面区域，该区域作为 1:1 复合物与四聚体 CII 结合。
