Human Cardiac Troponin I: A Langmuir Monolayer Study

Abstract

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.

Human islet amyloid polypeptide at the air–aqueous interface: a Langmuir monolayer approach

“…The surface potential-area isotherm was also correlated with the surface pressure-area isotherm as shown in figure 1b. Because the surface potential measures the dipole -dipole interactions at much longer distances than the interactions measured by surface pressure (usually owing to van der Waals interactions), the surface potential-area isotherm showed an increase in the surface potential as soon as the compression of the monolayer was started [53]. The collapse surface potential on pure water was observed at about 270 mV, much higher than that on the subphase that contained NaCl.…”

Immbolization of uricase enzyme in Langmuir and Langmuir-Blodgett films of fatty acids: Possible use as a uric acid sensor

“…In both cases, the film had hydrophobic groups on the surface, which may affect the conformation and orientation of the enzyme. The position of amide I for a-helix structures ranged between 1645 and 1658 cm À1 [26] for 3 out of the four films studied. The C@O stretching vibration for b-sheets has two main contributions: a strong one at $1630 cm À1 and a weaker one at $1690 cm À1 or $1650 cm À1 for antiparallel or parallel b-sheets, respectively.…”

Intrinsic disorder of the bacterial cell division protein ZipA: coil‐to‐brush conformational transition

“…The use of physicochemical tools as a probe of conformational properties of adsorbed proteins at fluid interfaces is already longstanding (32). However, most of those studies deal with globular proteins (33)(34)(35)(36)(37). In the world of unstructured proteins, to the best of our knowledge, only the case of ␤-casein has been addressed (38 -41).…”