Conformation of Apolipoprotein A-I and Its Interaction with Lipid Membrane

Tanaka Masafumi

doi:10.5360/membrane.32.253

Interaction of apolipoprotein (apo) A-I with lipid membrane is involved in a large number of processes in lipoprotein metabolism and cholesterol homeostasis. This review discusses the molecular mechanisms of interaction of apoA-I with lipid membrane in view of their structures. Lipid-free apoA-I is folded into two domains, comprising an Nterminal part forming a four-helix bundle and a discrete C-terminal part. It is well known that insertion of a proline residue into a protein sequence disruptsα-helix structure. Perturbation of the helix bundle structure occurs by the proline insertion into the putative helical region in the N-terminal domain, suggesting that the substituted residue is part of the helix bundle. In lipid-binding, apoA-I recognizes headgroup separation (hydrated space) between phospholipid molecules at the lipid membrane. ApoA-I initially binds to lipid through the C-terminal domain, followed by a conformational opening of the helix bundle with an accompanying increase inα-helical content. The transition from random coil toα-helix has been shown to produce a large negative enthalpy (exothermic heat) that drives lipid binding. Despite a lack of the C-terminal domain, which is critical for lipid-binding, perturbation of the helix bundle structure restored the lipidbinding ability by exposing a potential lipid-binding region in the N-terminal domain.

Conformation of Apolipoprotein A-I and Its Interaction with Lipid Membrane

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