Fluorescence evidence of annexin A6 translocation across membrane in model matrix vesicles during apatite formation

Matrix vesicles (MVs) are 100–300 nm spherical structures released by mineralization competent cells to initiate formation of apatite, the mineral component in bones. Among proteins present MVs, annexin A6 (AnxA6) is thought be ubiquitously distributed MVs’ lumen, on surface internal and external leaflets membrane also inserted lipid bilayer. To determine molecular mechanism(s) that lead different locations AnxA6, we hypothesized occurrence a pH drop during mineralization. Such change would induce AnxA6 protonation, which turn, because its isoelectric point 5.41, protein hydrophobicity facilitating insertion into The various distributions likely disturb phospholipid organization. examine this possibility, used fluorescein as reporter, established decreased inside MVs apatite formation. Then, 4-(14-phenyldibenzo[a,c]phenazin-9(14H)-yl)-phenol, vibration-induced emission fluorescent probe, was reporter changes organization occurring with varying mode binding. Proteoliposomes containing 1,2-Dimyristoyl-sn-glycero-3phosphocholine (DMPC) or 1,2-Dimyristoyl-sn-glycero-3phosphocholine: 1,2-Dipalmitoyl-sn-glycero-3-phosphoserine (DMPC:DPPS 9:1), mimic MV leaflet, respectively, served biomimetic models investigate nature Addition Anx6 DMPC at 7.4 5.4, DMPC:DPPS (9:1) induced decrease fluidity, consistent interactions bilayer surface. In contrast, addition 5.4 increased fluidity membrane. This latest result interpreted reflecting Taken together, these findings possible mechanism translocation from leaflet stimulated upon acidification lumen apatite.