Department of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA 02155, USA.
Biomaterials. 2010 Apr;31(10):2926-33. doi: 10.1016/j.biomaterials.2009.12.026. Epub 2009 Dec 30.
The anti-parallel beta pleated sheet is a fundamental secondary structure in proteins and a major component in silk fibers generated by silkworms and spiders, with a key role to stabilize these proteins via physical cross-links. Importantly, these beta-sheets are fully degradable and nontoxic structures in biology, in contrast for example to beta-amyloid structures formed in disease states. Thus, insight into mechanism of enzymatic degradation would be instructive as a route to elucidating differences among these stable yet different structural features in biological systems. We report on the mechanism of enzymatic degradation of anti-parallel beta pleated sheets with Bombyx mori silk structures, leading to fibrils and subsequently to nanofilaments (2nm thickness and 160nm length). These nanofilaments play a role as nucleators of the crystalline regions, an important feature of the system that can be exploited to design silk-based biomaterials with predictable biodegradability and mechanical properties. The potential toxicity of degradation products from these proteolytic enzymes was also assessed in vitro and no cell toxicity found in vitro for the protease found in vivo in the human body. The degradation mechanism of beta-sheet silk crystals provides additional insight into the significant differences in biological impact between the anti-parallel beta-sheet silk biomaterials reported in this work vs. amyloid structures in disease states, adding to prior descriptions of chemical and structural differences that are more extensively documented.
反平行β折叠片是蛋白质的基本二级结构，也是家蚕和蜘蛛产生的丝纤维的主要成分，通过物理交联稳定这些蛋白质。重要的是，与疾病状态下形成的β-淀粉样结构等相比，这些β-折叠片在生物学中是完全可降解且无毒的结构。因此，深入了解酶促降解的机制将有助于阐明生物系统中这些稳定但不同结构特征之间的差异。我们报告了丝素结构中反平行β折叠片的酶促降解机制，导致纤维和随后的纳米纤维（2nm 厚度和 160nm 长度）。这些纳米纤维作为结晶区的成核剂发挥作用，这是该系统的一个重要特征，可以用来设计具有可预测生物降解性和机械性能的基于丝素的生物材料。还评估了这些蛋白水解酶的降解产物的潜在毒性，并且在体内发现的蛋白酶在体外没有发现细胞毒性。β-片层丝晶的降解机制进一步深入了解了本工作中报道的反平行β-片层丝生物材料与疾病状态下的β-淀粉样结构之间在生物学影响方面的显著差异，补充了先前更广泛记录的化学和结构差异的描述。
