XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Ab initio and density functional calculation of calcium binding sphingomyelin lipid molecules: A pin holder model approach
Hiroyuki Kawabe1 and Kimikazu Sugimori2
1Department of Social Work, Faculty of Social Work, Kinjo University, Japan

2Department of Physical Therapy, Faculty of Health Sciences, Kinjo University, Japan
One of the phospholipids, sphingomyelin (SM, N-acyl-sphingosine-1-phosphorylcholine) is the most abundant component of mammalian membranes in brain and nervous tissues. It plays an important role for apoptosis, aging, signal transduction with cations. Recently, Yappert and co-workers have shown that human lens sphingomyelin and its hydrogenated derivative, dihydrosphingomyelin (DHSM) are interacted with Ca2+ ions to develop human cataracts [1,2]. Previously we have investigated conformational differences between an isolated SM / DHSM molecule and Ca2+ -coordinated form by using density functional theory (DFT) which B3LYP functional and 6-31G(d,p) double-zeta split-valence basis set is applied for geometry optimization and normal mode analysis. As a result, one of conformers of SMs has hydrogen bonding between hydroxyl group and phosphate group, whereas another conformer has hydrogen bonding between hydroxyl and phosphate amide group [3]. Moreover, 31P-Nuclear Magnetic Resonance (NMR) shielding constants of the obtained conformers are investigated by using ab initio and DFT with gauge invariant atomic orbitals (NMR-GIAO) calculations [4].
In this study, we apply previous results to dimer and trimer model of lipid molecules with Ca2+ and water molecules by quantum chemical calculations. We assume that tails of the lipids arbitrary fixed specific length in plasma membrane, like pin holder. Except for fixed tail groups, all of molecular structure of head group and solvated Ca2+ are fully optimized. We analyze potential energy surface (PES) with the fixed parameters that are length between tails of lipid and coordinate of Ca2+ approaching from outer region to phosphate.

References
[1] M. Rujoi, D. Borchman, D. B. Dupré, and M. C. Yappert, Biophys. J. 82 (2002) 3096-3104.
[2] M. C. Yappert and D. Borchman, Chem. Phys. Lipids 129 (2004) 1-20.
[3] K. Sugimori, H. Kawabe, H. Nagao and K. Nishikawa, Int. J. Quantum Chem. 108, 2935-2942 (2008). doi:10.1002/qua.21858
[4] K. Sugimori, H. Kawabe, H. Nagao, and K. Nishikawa, Int. J. Quantum Chem., 109 (2009) 3685-3693. doi:10.1002/qua.22404


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