Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, 142290 Moscow Region, Russia.
A.N. Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119991 Moscow Region, Russia.
Int J Mol Sci. 2023 Jan 5;24(2):1056. doi: 10.3390/ijms24021056.
A giant multidomain protein of striated and smooth vertebrate muscles, titin, consists of tandems of immunoglobulin (Ig)- and fibronectin type III (FnIII)-like domains representing β-sandwiches, as well as of disordered segments. Chicken smooth muscles express several titin isoforms of 500-1500 kDa. Using various structural-analysis methods, we investigated in vitro nonspecific amyloid aggregation of the high-molecular-weight isoform of chicken smooth-muscle titin (SMT, ~1500 kDa). As confirmed by X-ray diffraction analysis, under near-physiological conditions, the protein formed amorphous amyloid aggregates with a quaternary cross-β structure within a relatively short time (60 min). As shown by circular dichroism and Fourier-transform infrared spectroscopy, the quaternary cross-β structure-unlike other amyloidogenic proteins-formed without changes in the SMT secondary structure. SMT aggregates partially disaggregated upon increasing the ionic strength above the physiological level. Based on the data obtained, it is not the complete protein but its particular domains/segments that are likely involved in the formation of intermolecular interactions during SMT amyloid aggregation. The discovered properties of titin position this protein as an object of interest for studying amyloid aggregation in vitro and expanding our views of the fundamentals of amyloidogenesis.
一种存在于横纹肌和平滑肌中的巨大多功能蛋白，即原肌球蛋白，由串联的免疫球蛋白（Ig）和纤维连接蛋白 III（FnIII）样结构域组成，这些结构域代表β-三明治结构，以及无规片段。鸡的平滑肌表达几种约 500-1500 kDa 的原肌球蛋白同工型。我们使用各种结构分析方法，研究了鸡平滑肌原肌球蛋白（SMT，1500 kDa）的高分子量同工型在体外的非特异性淀粉样聚集。X 射线衍射分析证实，在近生理条件下，该蛋白在相对较短的时间内（60 分钟）形成无定形的淀粉样聚集，具有四元交叉-β结构。圆二色性和傅里叶变换红外光谱表明，与其他淀粉样变性蛋白不同，四元交叉-β结构的形成不会改变 SMT 的二级结构。当离子强度增加到生理水平以上时，SMT 聚集体部分解聚。基于获得的数据，可能是特定的结构域/片段而不是完整的蛋白参与了 SMT 淀粉样聚集过程中分子间相互作用的形成。原肌球蛋白的这些特性使其成为体外淀粉样聚集研究的一个有趣的对象，并扩展了我们对淀粉样变性基本原理的认识。
