Kamat Kartik, Naullage Pavithra M, Molinero Valeria, Peters Baron
Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, California 93106, United States.
Department of Chemistry, The University of Utah, Salt Lake City, Utah 84112, United States.
Biomacromolecules. 2022 Feb 14;23(2):513-519. doi: 10.1021/acs.biomac.1c01247. Epub 2021 Dec 20.
Some of the most potent antifreeze proteins (AFPs) are approximately rigid helical structures that bind with one side in contact with the ice surface at specific orientations. These AFPs take random orientations in solution; however, most orientations become sterically inaccessible as the AFP approaches the ice surface. The effect of these inaccessible orientations on the rate of adsorption of AFP to ice has never been explored. Here, we present a diffusion-controlled theory of adsorption kinetics that accounts for these orientational restrictions to predict a rate constant for adsorption (, in m/s) as a function of the length and width of the AFP molecules. We find that decreases with length and diameter of the AFP and is almost proportional to the inverse of the area of the binding surface. We demonstrate that the restricted orientations create an entropic barrier to AFP adsorption, which we compute to be approximately 7 T for most AFPs and up to 9 T for Maxi, the largest known AFP. We compare the entropic resistance 1/ to resistances for diffusion through boundary layers and across typical distances in the extracellular matrix and find that these entropic and diffusion resistances could become comparable in the small confined spaces of biological environments.
一些最有效的抗冻蛋白（AFP）是近似刚性的螺旋结构，其一侧以特定取向与冰表面接触结合。这些AFP在溶液中呈随机取向；然而，当AFP接近冰表面时，大多数取向在空间上变得无法接近。这些无法接近的取向对AFP吸附到冰上的速率的影响从未被探究过。在这里，我们提出了一种吸附动力学的扩散控制理论，该理论考虑了这些取向限制，以预测吸附速率常数（，单位为m/s）作为AFP分子长度和宽度的函数。我们发现随着AFP的长度和直径减小，并且几乎与结合表面面积的倒数成正比。我们证明受限取向为AFP吸附创造了一个熵垒，我们计算得出对于大多数AFP来说这个熵垒约为7 T，对于已知最大的AFP即Maxi来说高达9 T。我们将熵阻1/与通过边界层扩散以及在细胞外基质中的典型距离上的阻力进行比较，发现这些熵阻和扩散阻力在生物环境的小受限空间中可能变得相当。
