Human cardiac troponin I: a Langmuir monolayer study.
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.
Orbulescu
Jhony
J
University of Miami, Department of Chemistry, 1301 Memorial Drive, Coral Gables, Florida 33146, USA.
Micic
Miodrag
M
Ensor
Mark
M
Trajkovic
Sanja
S
Daunert
Sylvia
S
Leblanc
Roger M
RM
D000042:Absorption; D000388:Air; D001667:Binding, Competitive; D015374:Biosensing Techniques; D006801:Humans; D008853:Microscopy; D009206:Myocardium; D011312:Pressure; D055550:Protein Stability; D013055:Spectrophotometry, Infrared; D013499:Surface Properties; D019210:Troponin I / Q000737:chemistry* / Q000378:metabolism; D014867:Water / Q000737:chemistry
D019210:Troponin I; D014867:Water