We carry out in situ single-molecule measurements of the specific interaction between apolipoprotein A-I(apoA-I) and ATP binding cassette transporter A1(ABCA1) on THP-1 cells.Single-molecule force spectroscopy shows that similar to normal apoA-I,the dysfunctional apoA-I from diabetes patients interacts with ABCA1 via two different binding sites on the cells.The strength of dysfunctional apoA-I binding to a high-capacity binding site is 26.5±4.9 pN.The minor direct apoA-I/ABCA1 binding strength is 56.7±4.1 pN.These results facilitate a pathological understanding of the mechanisms that underlie the specific interaction of apoA-I and ABCA1 at the single-molecule level.
The mitochondria play essential roles in both intracellular calcium and reactive oxygen species signaling.As a newly discovered universal and fundamental mitochondrial phenomenon,superoxide flashes reflect transient bursts of superoxide production in the matrix of single mitochondria.Whether and how the superoxide flash activity is regulated by mitochondrial calcium remain largely unknown.Here we demonstrate that elevating mitochondrial calcium either by the calcium ionophore ionomycin or by increasing the bathing calcium in permeabilized HeLa cells increases superoxide flash incidence,and inhibition of the mitochondrial calcium uniporter activity abolishes the flash response.Quantitatively,the superoxide flash incidence is correlated to the steady-state mitochondrial calcium elevation with 1.7-fold increase per 1.0?F/F0 of Rhod-2 signal.In contrast,large mitochondrial calcium transients(e.g.,peak△F/F0~2.8,duration^2 min)in the absence of steady-state elevations failed to alter the flash activity.These results indicate that physiological levels of sustained,but not transient,mitochondrial calcium elevation acts as a potent regulator of superoxide flashes,but its mechanism of action likely involves a multi-step,slow-onset process.
