Fox CA, Ellison P, Ikon N, Ryan RO. Calcium-induced transformation of cardiolipin nanodisks.
Biochim Biophys Acta Biomembr 2019;
1861:1030-1036. [PMID:
30876942 DOI:
10.1016/j.bbamem.2019.03.005]
[Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 03/08/2019] [Accepted: 03/11/2019] [Indexed: 12/26/2022]
Abstract
Miniature membranes comprised of tetramyristoylcardiolipin (CL) and apolipoprotein (apo) A-I, termed nanodisks (ND), are stable, aqueous soluble, reconstituted high density lipoproteins. When CL ND, but not dimyristoylphosphatidylcholine (PC) ND, were incubated with CaCl2, a concentration dependent increase in sample turbidity occurred, consistent with CL undergoing a bilayer to non-bilayer transition. To assess the cation specificity of this reaction, CL ND were incubated with various mono- and divalent cations. Whereas monovalent cations had no discernable effect, MgCl2 and SrCl2 induced a response similar to CaCl2. When ND were formulated using different weight ratios of CL and PC, those possessing 100% CL or 75% CL remained susceptible to CaCl2 induced sample turbidity development while ND possessing 50% CL displayed reduced susceptibility. ND comprised of 25% CL and 75% PC were unaffected by CaCl2 under these conditions. SDS PAGE analysis of insoluble material generated by incubation of CL ND with CaCl2 revealed that nearly all apoA-I was recovered in the insoluble fraction along with CL. One h after addition of EDTA to CaCl2-treated CL ND, sample clarity was restored. Collectively, the data are consistent with a model wherein Ca2+ forms a bidentate interaction with anionic phosphates in the polar head group of CL. As phosphate group repositioning occurs to maximize Ca2+ binding, CL acyl chains reposition, accentuating the conical shape of CL to an extent that is incompatible with the ND bilayer structure.
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