Intrinsic Fluorescence Study of the Interaction of Human Apolipoprotein H with Phospholipid Vesicles

Abstract

Apolipoprotein H (ApoH) is a plasma glycoprotein with its in vivo physiological and pathogenic roles being closely related to its interaction with negatively charged membranes. In this paper, the interaction of ApoH with phospholipid vesicles was characterized by (i) detecting the wavelength shift of the fluorescence spectrum of ApoH and (ii) measuring the fluorescence quenching extent of ApoH by the membrane resident quencher 1-palmitoyl-2-stearoyl-(5-doxyl)-sn-glycero-3-phosphocholine (DPC). The observed blue shift upon addition of DMPG vesicles indicated that the tryptophan residues of ApoH moved from a polar to a nonpolar environment. The insertion ability of ApoH into PG-containing vesicles did not depend on the PG content in a stoichiometric way as did the blue shift, indicating that the negatively charged DMPG does not serve as a specific binding site but rather provides a suitable microenvironment for ApoH interaction. The finding that the detachment effect of cations on the blue shift is remarkably different from that on the quenching extent suggests that ApoH is capable of existing in two different conformations when membrane-bound.

Antiphospholipid reactivity against cardiolipin metabolites occurring during endothelial cell apoptosis

“…Considering that β 2 -GPI is normally present in concentrations of approximately 200 μg/ml in human sera, we performed immunostaining on TLC with sera that had been diluted to 1:1,000. With such a dilution, β 2 -GPI levels would fall below the minimum requirement (>0.5 μg/ml) for allowing binding of aCL to anionic phospholipids [39]. As previously demonstrated [40,41], TLC immunostaining showed a reactivity with CL and MCL up to a dilution of 1:1,000 (Figure 3c, lane 4), thereby excluding a major contribution of serum proteins to the observed immunoreactions to CL derivatives.…”

Insights into the pathophysiology of the antiphospholipid syndrome provided by atomic force microscopy

“…Hamdan et al, (2007) corroborated that large-scale conformational changes of β 2 GPI occur upon binding to a target membrane. Their findings also support the premise that binding to lipid presents more than one conformational possibility (Bouma et al, 1999; Wang et al, 1999). More recently, convincing evidence has been presented that β 2 GPI circulates in plasma in a circular conformation and that the protein opens up when it binds to phospholipid bilayers (Agar et al, 2010).…”

The ω-Loop Region of the Human Prothrombin γ-Carboxyglutamic Acid Domain Penetrates Anionic Phospholipid Membranes

“…The fractional accessibilities were 0.63 Ϯ 0.18 and 0.37 Ϯ 0.18, respectively. A decrease in K SV reflects a decrease in solvent exposure of the tryptophan or a decrease in tryptophan lifetime (45,46). However, lifetime is often associated with fluorescence intensity upon binding lipid vesicles (46).…”