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Fig. 5 | BMC Biology

Fig. 5

From: Functional analyses of phosphatidylserine/PI(4)P exchangers with diverse lipid species and membrane contexts reveal unanticipated rules on lipid transfer

Fig. 5

Analysis of the relationship between ORD’s affinity for PS and PI(4)P and its ability to transfer these lipids between membranes. a Description of the kinetic model. Osh6p or ORD8 (ORD) interacts with the same affinity with two distinct membranes A and B, each harboring a PS and PI(4)P pool, and can extract and release PS and PI(4)P. ORD-PS and ORD-PI(4)P correspond to the ORD in 1:1 complex with PS and PI(4)P, respectively. All kON and kOFF rates were set to 10 μM−1 s−1, and 1 s−1, respectively, unless otherwise specified. b Initial PS transfer rate (gray dots) as a function of kON-PS values (ranging from 0.01 to 10,000 μM−1 s−1), under the condition where the A membrane initially contained 5% PS and B membrane was devoid of PI(4)P (non-exchange condition). Initial PS (pink dots) and PI(4)P transfer rates (orange dots) were also calculated as a function of kON-PS, considering that PS and PI(4)P were initially present at 5% in the A and B membranes, respectively (exchange condition). PI(4)P transfer rate simulated with A membrane devoid of PS (non-exchange condition) was indicated by a dashed line. The gray areas correspond to regimes where kON-PS > kON-PI(4)P, i.e., the ORD has more affinity for PS than PI(4)P. The acceleration factors, calculated for PS and PI(4)P, correspond to the ratio (in log value) between the transfer rates derived from simulations performed in exchange and non-exchange conditions. c Acceleration factors of PS and PI(4)P transfer in exchange conditions, established for Osh6p and ORD8 with different PS species and 16:0/16:0-PI(4)P, are plotted against each other as in the Fig. 1e. For comparison, theoretical acceleration factors of PS and PI(4)P transfer, considering kON-PS value ranging from 0.01 to 10,000 μM−1 s−1 and a kON-PI(4)P value of 75 μM−1 s−1 for Osh6p or 40 μM−1 s−1 for ORD8, are plotted against each other (Osh6p, green; ORD8, blue)

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