Interfacial pH during mussel adhesive plaque formation

Mussel (Mytilus californianus) adhesion to marine surfaces involves an intricate and adaptive synergy of molecules and spatio-temporal processes. Although the molecules, such as mussel foot proteins (mfps), are well characterized, deposition details remain vague and speculative. Developing methods for the precise surveillance of conditions that apply during mfp deposition would aid both in understanding mussel adhesion and translating this adhesion into useful technologies. To probe the interfacial pH at which mussels buffer the local environment during mfp deposition, a lipid bilayer with tethered pH-sensitive fluorochromes was assembled on mica. The interfacial pH during foot contact with modified mica ranged from 2.2 to 3.3, which is well below the seawater pH of ~ 8. The acidic pH serves multiple functions: it limits mfp-Dopa oxidation, thereby enabling the catecholic functionalities to adsorb to surface oxides by H-bonding and metal ion coordination, and provides a solubility switch for mfps, most of which aggregate at pH ≥ 7–8.加州贻贝（Mytilus californianus）与海洋表面的粘附过程，依赖于分子与时空进程间复杂且具有适应性的协同效应。尽管贻贝足丝蛋白（mussel foot proteins, mfps）这类粘附分子已得到充分表征，但其沉积过程的细节仍模糊不明且多为推测性论断。开发可精准监测贻贝足丝蛋白沉积时各项环境条件的方法，既有助于深入阐明贻贝粘附机制，也能推动该粘附特性向实用技术的转化。为探究贻贝在足丝蛋白沉积过程中对局部环境进行pH缓冲的界面pH值，研究人员在云母（mica）表面组装了带有锚定型pH敏感荧光染料（pH-sensitive fluorochromes）的脂质双层。实验测得，贻贝足部与修饰后的云母接触时的界面pH范围为2.2至3.3，远低于海水约8的典型pH值。该酸性pH环境具备多重功能：既可抑制贻贝足丝蛋白中的多巴（Dopa）氧化，使儿茶酚官能团能够通过氢键与金属离子配位作用吸附于表面氧化物；还可为贻贝足丝蛋白提供溶解度调控开关——这类蛋白大多会在pH≥7~8的环境中发生聚集。