In vitro modeling of matrix vesicle nucleation: synergistic stimulation of mineral formation by annexin A5 and phosphatidylserine.
Annexins A5, A2, and A6 (Anx-A5, -A2, and -A6) are quantitatively major proteins of the matrix vesicle nucleational core that is responsible for mineral formation. Anx-A5 significantly activated the induction and propagation of mineral formation when incorporated into synthetic nucleation complexes made of amorphous calcium phosphate (ACP) and Anx-A5 or of phosphatidylserine (PS) plus ACP (PS-CPLX) and Anx-A5. Incorporation of Anx-A5 markedly shortened the induction time, greatly increasing the rate and overall amount of mineral formed when incubated in synthetic cartilage lymph. Constructed by the addition of Ca(2+) to PS, emulsions prepared in an intracellular phosphate buffer matched in ionic composition to the intracellular fluid of growth plate chondrocytes, these biomimetic PS-CPLX nucleators had little nucleational activity. However, incorporation of Anx-A5 transformed them into potent nucleators, with significantly greater activity than those made from ACP without PS. The ability of Anx-A5 to enhance the nucleation and growth of mineral appears to stem from its ability to form two-dimensional crystalline arrays on PS-containing monolayers. However, some stimulatory effect also may result from its ability to exclude Mg(2+) and HCO(-)(3) from nucleation sites. Comparing the various annexins for their ability to activate PS-CPLX nucleation yields the following: avian cartilage Anx-A5 > human placental Anx-A5 > avian liver Anx-A5 > or = avian cartilage Anx-A6 >> cartilage Anx-A2. The stimulatory effect of human placental Anx-A5 and avian cartilage Anx-A6 depended on the presence of PS, since in its absence they either had no effect or actually inhibited the nucleation activity of ACP. Anx-A2 did not significantly enhance mineralization.
Genge
Brian R
BR
Department of Chemistry and Biochemistry, Graduate Science Research Center, University of South Carolina, Columbia, South Carolina 29208, USA.
Wu
Licia N Y
LN
Wuthier
Roy E
RE
D000818:Animals; D017306:Annexin A2 / Q000737:chemistry / Q000378:metabolism; D017304:Annexin A5 / Q000737:chemistry* / Q000378:metabolism; D017317:Annexin A6 / Q000737:chemistry / Q000378:metabolism; D001639:Bicarbonates / Q000737:chemistry / Q000378:metabolism; D002113:Calcification, Physiologic; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002413:Cations, Divalent / Q000737:chemistry / Q000378:metabolism; D019902:Chondrocytes / Q000737:chemistry / Q000378:metabolism; D003460:Crystallization; D004655:Emulsions / Q000737:chemistry; D006801:Humans; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism; D008567:Membranes, Artificial; D008954:Models, Biological; D010718:Phosphatidylserines / Q000737:chemistry* / Q000378:metabolism
D017306:Annexin A2; D017304:Annexin A5; D017317:Annexin A6; D001639:Bicarbonates; D002413:Cations, Divalent; D004655:Emulsions; D008567:Membranes, Artificial; D010718:Phosphatidylserines; D008274:Magnesium; D002118:Calcium