Division of Theoretical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00, Lund, Sweden.
Institut Laue-Langevin, 71 avenue des Martyrs, 38000, Grenoble, France.
Langmuir. 2023 Jun 6;39(22):7694-7706. doi: 10.1021/acs.langmuir.3c00498. Epub 2023 May 25.
Histatin 5 is a histidine-rich, intrinsically disordered, multifunctional saliva protein known to act as a first line of defense against oral candidiasis caused by . An earlier study showed that, upon interaction with a common model bilayer, a protein cushion spontaneously forms underneath the bilayer. Our hypothesis is that this effect is of electrostatic origin and that the observed behavior is due to proton charge fluctuations of the histidines, promoting attractive electrostatic interactions between the positively charged proteins and the anionic surfaces, with concomitant counterion release. Here we are investigating the role of the histidines in more detail by defining a library of variants of the peptide, where the former have been replaced by the pH-insensitive amino acid glutamine. By using experimental techniques such as circular dichroism, small angle X-ray scattering, quartz crystal microbalance with dissipation monitoring, and neutron reflectometry, it was determined that changing the number of histidines in the peptide sequence did not affect the structure of the peptide dissolved in solution. However, it was shown to affect the penetration depth of the peptide into the bilayer, where all variants except the one with zero histidines were found below the bilayer. A decrease in the number of histidine from the original seven to zero decreases the ability of the peptide to penetrate the bilayer, and the peptide is then also found residing within the bilayer. We hypothesize that this is due to the ability of the histidines to charge titrate, which charges up the peptide, and enables it to penetrate and translocate through the lipid bilayer.
组蛋白 5 是一种富含组氨酸的、固有无序的多功能唾液蛋白，已知它可以作为抵御由引起的口腔念珠菌病的第一道防线。早期的研究表明，当与常见的模型双层相互作用时，蛋白质垫会在双层下方自发形成。我们的假设是，这种效应具有静电起源，并且观察到的行为是由于组氨酸的质子电荷波动，促进了带正电荷的蛋白质与阴离子表面之间的吸引力静电相互作用，同时伴随抗衡离子的释放。在这里，我们通过定义该肽的变体文库更详细地研究了组氨酸的作用，其中前组氨酸已被 pH 不敏感的氨基酸谷氨酰胺取代。通过使用圆二色性、小角 X 射线散射、石英晶体微天平耗散监测和中子反射测量等实验技术，确定改变肽序列中的组氨酸数量不会影响溶解在溶液中的肽的结构。然而，它被证明会影响肽进入双层的穿透深度，除了零个组氨酸的变体之外，所有变体都被发现在双层下方。从原始的七个组氨酸减少到零个组氨酸数量会降低肽穿透双层的能力，并且肽也被发现在双层内。我们假设这是由于组氨酸的荷电滴定能力，它使肽带电荷，并使它能够穿透并通过脂质双层转运。
