Department of Physics and Astronomy, Rice University, Houston, Texas, USA.
Biophys J. 2011 Apr 6;100(7):1688-96. doi: 10.1016/j.bpj.2011.02.018.
Human LL-37 is a multifunctional cathelicidin peptide that has shown a wide spectrum of antimicrobial activity by permeabilizing microbial membranes similar to other antimicrobial peptides; however, its molecular mechanism has not been clarified. Two independent experiments revealed LL-37 bound to membranes in the α-helical form with the axis lying in the plane of membrane. This led to the conclusion that membrane permeabilization by LL-37 is a nonpore carpet-like mechanism of action. Here we report the detection of transmembrane pores induced by LL-37. The pore formation coincided with LL-37 helices aligning approximately normal to the plane of the membrane. We observed an unusual phenomenon of LL-37 embedded in stacked membranes, which are commonly used in peptide orientation studies. The membrane-bound LL-37 was found in the normal orientation only when the membrane spacing in the multilayers exceeded its fully hydrated value. This was achieved by swelling the stacked membranes with excessive water to a swollen state. The transmembrane pores were detected and investigated in swollen states by means of oriented circular dichroism, neutron in-plane scattering, and x-ray lamellar diffraction. The results are consistent with the effect of LL-37 on giant unilamellar vesicles. The detected pores had a water channel of radius 23-33 Å. The molecular mechanism of pore formation by LL-37 is consistent with the two-state model exhibited by magainin and other small pore-forming peptides. The discovery that peptide-membrane interactions in swollen states are different from those in less hydrated states may have implications for other large membrane-active peptides and proteins studied in stacked membranes.
人 LL-37 是一种多功能的抗菌肽，它通过类似于其他抗菌肽的方式破坏微生物膜的通透性而显示出广谱的抗菌活性；然而，其分子机制尚未阐明。两项独立的实验表明，LL-37 以α-螺旋的形式与膜结合，其轴位于膜的平面内。这导致了这样的结论：LL-37 通过非孔状地毯样作用机制破坏细胞膜的通透性。在这里，我们报告了检测到由 LL-37 诱导的跨膜孔。孔的形成与 LL-37 螺旋大约垂直于膜的平面排列一致。我们观察到了一个不寻常的现象，即 LL-37 嵌入堆叠的膜中，这在肽定向研究中很常见。只有当多层膜中的膜间距超过其完全水合的值时，才能发现膜结合的 LL-37 处于正常取向。这是通过用过量的水将堆叠的膜溶胀到溶胀状态来实现的。通过定向圆二色性、平面内中子散射和 X 射线层状衍射，在溶胀状态下检测和研究了跨膜孔。结果与 LL-37 对巨大的单层囊泡的影响一致。检测到的孔的水通道半径为 23-33Å。LL-37 形成孔的分子机制与抗菌肽和其他小的孔形成肽所表现出的两态模型一致。在溶胀状态下肽-膜相互作用不同于在水合状态下的发现，这可能对在堆叠膜中研究的其他大的膜活性肽和蛋白质具有意义。
