Journal
LANGMUIR
Volume 26, Issue 5, Pages 3268-3274Publisher
AMER CHEMICAL SOC
DOI: 10.1021/la903033x
Keywords
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Funding
- University of Miami, College of Arts and Sciences
- National Science Foundation [CBET-0944290]
- National Institutes of Health
- National Acronautics and Space Administration
- Gill Eminent Professorship
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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 it 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.
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