Beta‐2‐glycoprotein I (β2GPI) is the major antigen for the antiphospholipid antibodies in the antiphospholipid syndrome. The exposed epitope in domain I of β2GPI can be recognized by the anti‐β2GPI antibody. Here, we prepared the anionic di‐oleoyl‐phosphatidylserine (DOPS) and cardiolipin (CL) liposomes to interact with the β2GPI. The conformational changes of β2GPI upon binding with the liposomes were analyzed using hydrogen/deuterium exchange mass spectrometry. The exchange level of sequences 21–27 significantly increased after β2GPI had interacted with DOPS. This change indicated a reduced interaction between domain I and domain V, inferring to a protrusion of the sequences 21–27 from the ring conformation. After β2GPI had interacted with CL for 30 min, the exchange levels in 4 of the 5 domains increased significantly. The deuteration levels of sequences 1–20, 21–27, 196–205, 273–279 and 297–306 increased, suggesting that these regions had become more exposed, and the domain I was no longer in contact with domain V. The increasing deuteration levels in sequences 70–86, 153–162, 191–198, 196–205 and 273–279 indicated β2GPI undergoing conformational changes to expose these inner regions, suggesting a structural transition. Overall, DOPS and CL induced minor conformational changes of β2GPI at sequences 21–27 and forms an intermediate conformation after 10 min of interaction. After a complete protein–lipid interaction, high negatively charged CL membrane induced a major conformation transition of β2GPI.

The zebrafish (Danio rerio) is an important and widely used vertebrate model organism for the study of human diseases which include disorders caused by dysfunctional mitochondria. Mitochondria play an essential role in both energy metabolism and apoptosis, which are mediated through a mitochondrial phospholipid cardiolipin (CL). In order to examine the cardiolipin profile in the zebrafish model, we developed a CL analysis platform by using liquid chromatography-mass spectrometry (LC-MS). Meanwhile, we tested whether chlorella diet would alter the CL profile in the larval fish, and in various organs of the adult fish. The results showed that chlorella diet increased the chain length of CL in larval fish. In the adult zebrafish, the distribution patterns of CL species were similar between the adult brain and eye tissues, and between the heart and muscles. Interestingly, monolyso-cardiolipin (MLCL) was not detected in brain and eyes but found in other examined tissues, indicating a different remodeling mechanism to maintain the CL integrity. While the adult zebrafish were fed with chlorella for four weeks, the CL distribution showed an increase of the species of saturated acyl chains in the brain and eyes, but a decrease in the other organs. Moreover, chlorella diet led to a decrease of MLCL percentage in organs except the non-MLCL-containing brain and eyes. The CL analysis in the zebrafish provides an important tool for studying the mechanism of mitochondria diseases, and may also be useful for testing medical regimens targeting against the Barth Syndrome.

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