University of Miami, Department of Chemistry, 1301 Memorial Drive, Coral Gables, Florida 33146, USA.
Langmuir. 2010 Mar 2;26(5):3268-74. doi: 10.1021/la903033x.
Human cardiac troponin I (cTnI) is the preferred biomarker in the assessment of myocardial infarction. It is known to interact with troponin C and T to form a trimeric complex. Whereas small amounts are found in the cytoplasm, most of cTnI is in the form of a complex with actin located in myofilaments. To understand these interactions of cTnI better, we first investigated the surface chemistry of cTnI as a Langmuir monolayer spread at the air-water interface. We investigated the optimal conditions for obtaining a stable Langmuir monolayer in terms of changing the ionic strength of the subphase using different concentrations of potassium chloride. Monolayer stability was investigated by compressing the cTnI monolayer to a specific surface pressure and keeping the surface pressure constant while measuring the decrease in the molecular area as a function of time. Aggregation and/or domain formation was investigated by using compression-decompression cycles, in situ UV-vis spectroscopy, Brewster angle microscopy (BAM), and epifluorescence microscopy. To ensure that the secondary structure is maintained, we used infrared reflection-absorption spectroscopy (IRRAS) directly at the air-subphase interface. It was found that cTnI forms a very stable monolayer (after more that 5000 s) that does not aggregate at the air-subphase interface. The cTnI molecules maintain their secondary structure and, on the basis of the low reflectivity observed using BAM measurements and the low reflection-absorption intensities measured with IRRAS spectroscopy, lie flat on the subphase with the alpha-helices parallel to the air-subphase interface.
人心肌肌钙蛋白 I（cTnI）是评估心肌梗死的首选生物标志物。已知它与肌钙蛋白 C 和 T 相互作用形成三聚体复合物。虽然细胞质中存在少量 cTnI，但大部分 cTnI 是以与位于肌原纤维中的肌动蛋白形成复合物的形式存在。为了更好地了解这些 cTnI 的相互作用，我们首先研究了 cTnI 作为在气-水界面上展开的 Langmuir 单层的表面化学。我们研究了通过使用不同浓度的氯化钾改变亚相的离子强度来获得稳定的 Langmuir 单层的最佳条件。通过将 cTnI 单层压缩到特定的表面压力并保持表面压力恒定，同时测量分子面积随时间的减少来研究单层稳定性。通过使用压缩-减压循环、原位紫外-可见光谱、布鲁斯特角显微镜（BAM）和荧光显微镜研究聚集和/或域形成。为了确保保持二级结构，我们直接在气-亚相界面使用红外反射吸收光谱（IRRAS）。结果发现，cTnI 形成非常稳定的单层（超过 5000 s 后），在气-亚相界面上不会聚集。cTnI 分子保持其二级结构，并且基于 BAM 测量观察到的低反射率和 IRRAS 光谱测量到的低反射吸收强度，它们以平行于气-亚相界面的α-螺旋的方式平躺于亚相上。
