Functional identification of α1-giardin as an annexin of Giardia lamblia

Abstract

A protein with a relative molecular mass of 31 kDa was specifically extracted by EGTA from a detergent-insoluble fraction of Giardia lamblia. N-terminal sequencing showed this protein to be identical to α1-giardin, a component of the ventral disc which, based on its predicted amino acid sequence, has been classified as annexin XIX. Purified α1-giardin associated with multilamellar phosphatidyl serine-containing vesicles in a Ca2+-dependent manner, confirming that it is a functional annexin. Molecular modelling of the amino acid sequence of the giardial annexin into the X-ray structure of annexin V suggests that the Ca2+-binding sites, which, as in other annexins, are all located on the convex surface of the molecule, are of the low-affinity type III. Copyright (C) 1999 Federation of European Microbiological Societies.