Functional identification of alpha 1-giardin as an annexin of Giardia lamblia

A protein with a relative molecular mass of 31 kDa was specifically extract ed by EGTA from a detergent-insoluble fraction of Giardia lamblia. N-termin al sequencing showed this protein to be identical to alpha 1-giardin, a com ponent of the ventral disc which, based on its predicted amino acid sequenc e, has been classified as annexin XIX. Purified alpha 1-giardin associated with multilamellar phosphatidyl serine-containing vesicles in a Ca2+-depend ent manner, confirming that it is a functional annexin. Molecular modelling of the amino acid sequence of the giardial annexin into the X-ray structur e of annexin V suggests that the Ca2+-binding sites, which, as in other ann exins, are all located on the convex surface of the molecule, are of the lo w-affinity type III. (C) 1999 Published by Elsevier Science B.V. All rights reserved.