Annexin V interactions with collagen.
Annexin V was originally identified as a collagen-binding protein called anchorin CII and was isolated from chondrocyte membranes by affinity chromatography on native type II collagen. The binding of annexin V to native collagen type II is stable at physiological ionic strength when annexin V is reconstituted in liposomes. The binding to native collagen types II and X, and to some extent to type I as well, was confirmed using recombinant annexin V. A physiological role for annexin V interactions with extracellular collagen is consistent with the localization of annexin V on the outer cell surface of chondrocytes, microvilli of hypertrophic chondrocytes, fibroblasts and osteoblasts. A breakthrough in our understanding of the function of annexin V was made with the discovery of its calcium channel activity. At least one of several putative functions of annexin V became obvious from studies on matrix vesicles derived from calcifying cartilage. It was found that calcium uptake by matrix vesicles depend on collagen type II and type X binding to annexin V in the vesicles and was lost when collagens were digested with collagenase: calcium influx was reconstituted after adding back native collagen II or V. These findings indicate that annexin V plays a major role in matrix vesicle-initiated cartilage calcification as a collagen-regulated calcium channel.
von der Mark
K
K
Institute of Experimental Medicine, Friedrich-Alexander University of Erlangen-Nürnberg, Germany. kvdmark@EXPMED.UNI-ERLANGEN.DE
Mollenhauer
J
J
D000818:Animals; D017304:Annexin A5 / Q000378:metabolism*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003094:Collagen / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans
D017304:Annexin A5; D003094:Collagen; D002118:Calcium