Samartzidou H, Delcour A H
Department of Biology and Biochemistry, University of Houston, TX 77204-5513, USA.
FEBS Lett. 1999 Feb 5;444(1):65-70. doi: 10.1016/s0014-5793(99)00030-7.
The inhibition of the anion-selective PhoE porin by ATP and of the cation-selective OmpF porin by polyamines has been previously documented. In the present study, we have extended the comparison of the inhibitor-porin pairs by investigating the effect of anions (ATP and aspartate) and positively charged polyamines (spermine and cadaverine) on both OmpF and PhoE with the patch-clamp technique, and by comparing directly the gating kinetics of the channels modulated by their respective substrates. The novel findings reported here are (1) that the activity of PhoE is completely unaffected by polyamines, and (2) that the kinetic changes induced by ATP on PhoE or polyamines on OmpF suggest different mechanisms of inhibition. ATP induces a high degree of flickering in the PhoE-mediated current and appears to behave as a blocker of ion flow during its presumed transport through PhoE. Polyamines modulate the kinetics of openings and closings of OmpF, in addition to promoting a blocker-like flickering activity. The strong correlation between sensitivity to inhibitors and ion selectivity suggests that some common molecular determinants are involved in these two properties and is in agreement with the hypothesis that polyamines bind inside the pore of cationic porins.
先前已有文献记载ATP对阴离子选择性的PhoE孔蛋白的抑制作用以及多胺对阳离子选择性的OmpF孔蛋白的抑制作用。在本研究中，我们通过膜片钳技术研究阴离子（ATP和天冬氨酸）和带正电荷的多胺（精胺和尸胺）对OmpF和PhoE的影响，以及直接比较由各自底物调节的通道的门控动力学，扩展了对抑制剂-孔蛋白对的比较。此处报道的新发现为：（1）PhoE的活性完全不受多胺影响；（2）ATP对PhoE或多胺对OmpF诱导的动力学变化表明存在不同的抑制机制。ATP在PhoE介导的电流中诱导高度闪烁，并且在其假定通过PhoE转运期间似乎表现为离子流的阻断剂。多胺除了促进类似阻断剂的闪烁活性外，还调节OmpF开放和关闭的动力学。对抑制剂的敏感性与离子选择性之间的强相关性表明，这两种特性涉及一些共同的分子决定因素，这与多胺结合在阳离子孔蛋白孔内的假设一致。
