Abstract
Tomato annexin p35 has been cloned and used in a site-directed mutagenesis study to explore the phospholipid binding and catalytic properties of the protein in detail. Analysis of the cDNA sequence of p35 reveals that the annexin has only two typical endonexin folds, corresponding to repeats I and IV. Expression of recombinant p35 in Escherichia coli confirmed both phospholipid binding and a nucleotide phosphatase activity that could be inhibited on interaction of the recombinant annexin with phospholipids. Site-directed mutagenesis in which the acidic residues Glu-68 (repeat I), and Asp-297 (repeat IV) were changed to Asn, generated two mutant forms, E68N and D297N, respectively. Both mutant forms of the annexin continued to express catalytic activity. Changing repeat I had little effect on phospholipid binding, whereas the change to repeat IV abolished this property. These data show that, in this plant annexin, repeat IV plays a more critical role in calcium-dependent phospholipid binding than repeat I, and that the catalytic and phospholipid binding activity of the protein can be separated experimentally.
Highlights
Tomato annexin p35 has been cloned and used in a site-directed mutagenesis study to explore the phospholipid binding and catalytic properties of the protein in detail
Expression of recombinant p35 in Escherichia coli confirmed both phospholipid binding and a nucleotide phosphatase activity that could be inhibited on interaction of the recombinant annexin with phospholipids
This study describes the cloning, heterologous expression, and biochemical analysis of the recombinant p35 annexin of tomato plants
Summary
Tomato annexin p35 has been cloned and used in a site-directed mutagenesis study to explore the phospholipid binding and catalytic properties of the protein in detail. Site-directed mutagenesis in which the acidic residues Glu-68 (repeat I), and Asp297 (repeat IV) were changed to Asn, generated two mutant forms, E68N and D297N, respectively Both mutant forms of the annexin continued to express catalytic activity. Subsequent analysis of a number of annexin sequences revealed significant homology predominantly in the core domain that comprises four conserved repeats (or eight repeats in annexin VI). These repeats are approximately 70 amino acids in length. Proteins were implicated in secretory processes (8 –11); more recently, plant annexins have been reported to regulate the activity of the cell surface enzyme involved in [133]--glucan (callose) synthesis [12], as well as exhibiting several catalytic activities of their own, including ATPase and peroxidase activities [13,14]
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