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BMC Evolutionary Biology

, 10:43

First Online: 14 February 2010Received: 06 November 2009Accepted: 14 February 2010


BackgroundConger eel galectins, congerin I ConI and congerin II ConII, show the different molecular characteristics resulting from accelerating evolution. We recently reconstructed a probable ancestral form of congerins, Con-anc. It showed properties similar to those of ConII in terms of thermostability and carbohydrate recognition specificity, although it shares a higher sequence similarity with ConI than ConII.

ResultsIn this study, we have focused on the different amino acid residues between Con-anc and ConI, and have performed the protein engineering of Con-anc through site-directed mutagenesis, followed by the molecular evolution analysis of the mutants. This approach revealed the functional importance of loop structures of congerins: 1 N- and C-terminal and loop 5 regions that are involved in conferring a high thermostability to ConI; 2 loops 3, 5, and 6 that are responsible for stronger binding of ConI to most sugars; and 3 loops 5 and 6, and Thr38 residue in loop 3 contribute the specificity of ConI toward lacto-N-fucopentaose-containing sugars.

ConclusionsThus, this methodology, with tracing of the molecular evolution using ancestral mutants, is a powerful tool for the analysis of not only the molecular evolutionary process, but also the structural elements of a protein responsible for its various functions.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2148-10-43 contains supplementary material, which is available to authorized users.

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Autor: Ayumu Konno - Shintarou Yonemaru - Atsushi Kitagawa - Koji Muramoto - Tsuyoshi Shirai - Tomohisa Ogawa


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