A fluorometric assay for lysosomal phospholipase A2 activity using fluorescence-labeled truncated oxidized phospholipid

Membrane phosphatidylserine allosterically regulates the cytosolic phospholipase A2 activity via an electrostatic-switch mechanism

Phospholipase A2 (PLA2) is a peripheral membrane protein that plays an essential role in many inflammatory responses. However, the activation mechanisms of PLA2 on the membrane surface have not been fully understood. Herein, we have combined experimental techniques and theoretical approaches to investigate the activation and association of the PLA2 protein on an artificial phospholipid membrane. Using a phosphatidylserine (PS) nanodomain containing membrane to mimic the inflammatory conditions, we found that the activity of cytosolic PLA2s (cPLA2s) increases with higher ratios of PS in the membrane. Molecular dynamics simulations reveal that significant changes in the protein structure are related to negatively charged membranes. In particular, the alteration of negatively charged residues in the C2 domain brings about an opened binding pocket and the catalytic site access to the substrate phospholipid. Meanwhile, the negative residues in the loop 650-665 facilitate the optimal interfacial orientation of the protein with a closed binding pocket on the membrane surface. These results lead us to suggest an electrostatic-switch allosteric mechanism for cPLA2 activation on the cell membrane surface under the inflammatory state.

Optical fiber bio-sensor for phospholipase using liquid crystal

A cost-effective and label-free optical fiber sensor was proposed to detect phospholipase A₂ (PLA₂) in nM concentration. The sensor is made of an alkoxysilane-modified side-polished fiber (SPF) coated with 4'-pentyl-4-cyanobiphenyl (5CB) and self-assembled phospholipid (L-DLPC). It is found that the relative transmission optical power (RTOP) of the fiber sensor decreases due to the 5CB realignment and redistribution induced by the PLA₂ hydrolysis of L-DLPC. The response-time at 5 dB RTOP variation exhibits an exponential dependence on PLA₂ concentration, allowing us to detect the PLA₂ by the 5 dB-response time. This detection method can reduce the detection time. Compare with the traditional copper-grid sensor, the proposed novel fiber sensor has a lower detection limit (<1 nM). Furthermore, the sensor has good repeat-ability and specificity.The sensor's RTOP variation for PLA₂ detection at 1 nM is ~21 times higher than that for five other enzymes (trypsin, amylase, thrombin, glucose oxidase, pepsin) at 1000 nM and lipase at 50 nM. This confirms the sensor's excellent PLA₂ specificity. The fiber sensor provides a potential way to be incorporated into micro-flow chips to quantitatively detect biological molecules in a real-time and online manner.