Distribution of phospholipid transfer protein in human plasma: presence of two forms of phospholipid transfer protein, one catalytically active and the other inactive

Abstract

Plasma phospholipid transfer protein (PLTP) plays an important role in the maintenance of plasma highdensity lipoprotein (HDL) content and remodeling of HDL in the circulation. In the present study we have used different fractionation methods to investigate the distribution of PLTP in human plasma. A novel enzyme-linked immunosorbent assay developed during the study allowed for simultaneous assessment of both PLTP mass and activity in the fractions obtained. Size-exclusion chromatography and plasma fractionation by nondenaturing polyacrylamide gel electrophoresis (PAGE) yielded similar results demonstrating that PLTP associates in native plasma with two distinct particle populations, while ultracentrifugation with high salt leads to detachment of PLTP from lipoprotein particles and loss of a majority of its phospholipid transfer activity. Interestingly, analysis of the size-exclusion chromatography fractions demonstrated that PLTP exists in the circulation as an active population that elutes in the position of HDL corresponding to an average molecular mass of 160 ؎ 40 kDa and an inactive form with an average mass of 520 ؎ 120 kDa. The inactive fraction containing approximately 70% of the total PLTP protein eluted between HDL and low density lipoprotein (LDL). Thus, the two PLTP pools are associated with different types of lipoprotein particles, suggesting that the PLTP activity in circulation is modulated by the plasma lipoprotein profile and lipid composition. -

ApoE-containing high density lipoproteins and phospholipid transfer protein activity increase in patients with a systemic inflammatory response

“…As the localization of PLTP and CETP in the lower molecular weight range differed in such a way that two different particles could be separated by 2D-GGE, with the PLTP spot having higher molecular mass and slow HDL mobility, these particles may represent either lipid-complexed proteins or homodimers. Oka et al (36) have demonstrated the presence of large (12-to 14-nm) particles with PLTP immunoreactivity. These particles carry an inactive form of PLTP, whereas the active form of PLTP was associated with smaller, 9-to 11-nm particles.…”

Differences in reactivity of antibodies to active versus inactive PLTP significantly impacts PLTP measurement

“…An alternative explanation for the presence of inactive and active PLTP may be that the conformation of PLTP may differ when it is associated with larger particles as compared with smaller ones, resulting in a loss of transfer activity as suggested by Oka et al (4). The binding of PLTP to particles with a certain radius of curvature may affect the conformation of PLTP in such a way that binding or efficient transfer of lipid is impeded.…”

“…Oka et al (3) carried out another study using a double monoclonal sandwich ELISA and also reported no correlation between PLTP mass and activity in a group of 132 Japanese subjects. Oka et al (4), using the double monoclonal sandwich ELISA system for detection of PLTP mass, went on to analyze the mass and activity of PLTP in lipoprotein fractions separated by fast protein liquid chromatography (FPLC). They reported a large discrepancy between the distribution of mass as compared with that of PLTP activity, with substantial mass being present in the LDL and very large HDL region and the majority of the activity being found in the region of small HDL.…”

Molecular characterization of rabbit phospholipid transfer protein: choroid plexus and ependyma synthesize high levels of phospholipid transfer protein

“…Given the fact that the protein content of normal rabbit cerebrospinal fluid is approximately two orders of magnitude lower than that of plasma (41) and assuming a normal specific activity of PLTP in cerebrospinal fluid, we estimate the relative PLTP concentration of rabbit cerebrospinal fluid to exceed that of plasma by at least 20-fold. If the cerebrospinal fluid, like plasma (48), were to contain both active and inactive forms of PLTP, extrapolation from activity to PLTP mass data would be further complicated. Even the relatively high PLTP activity in the cere- brospinal fluid need not be due necessarily to local PLTP synthesis, but could reflect efficient active transport from plasma.…”