Complex Roles of Hybrid Lipids in the Composition, Order, and Size of Lipid Membrane Domains

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• 作者：Ebrahim Hassan-Zadeh ; Eda Baykal-Caglar ; Mohammad Alwarawrah ; Juyang Huang
• 刊名：Langmuir
• 出版年：2014
• 出版时间：February 11, 2014
• 年：2014
• 卷：30
• 期：5
• 页码：1361-1369
• 全文大小：579K
• ISSN：1520-5827

文摘

Hybrid lipids (HL) are phospholipids with one saturated chain and one unsaturated chain. HL are hypothesized to act as linactants (i.e., 2D surfactants) in cell membranes, reducing line tension and creating nanoscopic lipid domains. Here we compare three hybrid lipids of different chain unsaturation (16:0鈥?8:1PC (POPC), 16:0鈥?8:2PC (PLPC), and 16:0鈥?0:4PC (PAPC)) in their abilities to alter the composition, line tension, order, and compactness of lipid domains. We found that the liquid-ordered (L_o) and liquid-disordered (L_d) lipid domains in PAPC/di18:0PC(DSPC)/cholesterol and PLPC/DSPC/cholesterol mixtures are micrometer-sized, and only the POPC/DSPC/cholesterol system has nanoscopic domains. The results indicate that some HLs with polyunsaturated chains are not linactants, and the monounsaturated POPC displays both properties of weak linactants and 鈥淟_d-phase鈥?lipids such as di18:1PC (DOPC). The obtained phase boundaries from giant unilamellar vesicles (GUV) show that both POPC and PLPC partition well in the L_o phases. Our MD simulations reveal that these hybrid lipids decrease the order and compactness of L_o domains. Thus, hybrid lipids distinguish themselves from other lipid groups in this combined 鈥減artitioning and loosening鈥?ability, which could explain why the L_o domains of GUVs, which often do not contain HL, are more compact than the raft domains in cell membranes. Our line tension measurement and Monte Carlo simulation both show that even the monounsaturated POPC is a weak linactant with only modest ability to occupy domain boundaries and reduce line tension. A more important property of HLs is that they can reduce physical property differences of L_o and L_d bulk domains, which also reduces line tension at domain boundaries.