Ipomoelin, a jacalin-related lectin with a compact tetrameric association and versatile carbohydrate binding properties regulated by its N terminus.

ABSTRACT: Many proteins are induced in the plant defense response to biotic stress or mechanical wounding. One group is lectins. Ipomoelin (IPO) is one of the wound-inducible proteins of sweet potato (Ipomoea batatas cv. Tainung 57) and is a Jacalin-related lectin (JRL). In this study, we resolved the crystal structures of IPO in its apo form and in complex with carbohydrates such as methyl ?-D-mannopyranoside (Me-Man), methyl ?-D-glucopyranoside (Me-Glc), and methyl ?-D-galactopyranoside (Me-Gal) in different space groups. The packing diagrams indicated that IPO might represent a compact tetrameric association in the JRL family. The protomer of IPO showed a canonical ?-prism fold with 12 strands of ?-sheets but with 2 additional short ?-strands at the N terminus. A truncated IPO (?N10IPO) by removing the 2 short ?-strands of the N terminus was used to reveal its role in a tetrameric association. Gel filtration chromatography confirmed IPO as a tetrameric form in solution. Isothermal titration calorimetry determined the binding constants (K(A)) of IPO and ?N10IPO against various carbohydrates. IPO could bind to Me-Man, Me-Glc, and Me-Gal with similar binding constants. In contrast, ?N10IPO showed high binding ability to Me-Man and Me-Glc but could not bind to Me-Gal. Our structural and functional analysis of IPO revealed that its compact tetrameric association and carbohydrate binding polyspecificity could be regulated by the 2 additional N-terminal ?-strands. The versatile carbohydrate binding properties of IPO might play a role in plant defense.

SUBMITTER: Chang WC 

PROVIDER: S-EPMC3394770 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature