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Journal of Biochemistry Advance Access originally published online on July 23, 2007
Journal of Biochemistry 2007 142(3):393-401; doi:10.1093/jb/mvm146
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© 2007 The Japanese Biochemical Society.

Elderberry Bark Lectins Evolved to Recognize Neu5Ac{alpha}2,6Gal/GalNAc Sequence from a Gal/GalNAc Binding Lectin Through the Substitution of Amino-Acid Residues Critical for the Binding to Sialic Acid

Hanae Kaku1,3,*, Hiroki Kaneko2,*, Naoto Minamihara3,4,*, Kazumichi Iwata3, Elizabeth T. Jordan3, Maria A. Rojo3, Naoko Minami-Ishii3, Eiichi Minami3, Shigeru Hisajima4 and Naoto Shibuya1,3,{dagger}

1Department of Life Sciences, Meiji University, Kawasaki, Kanagawa 214-8571; 2Department of Integrated Sciences in Physics and Biology, Nihon University, Tokyo 156-8550; 3Department of Biochemistry, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602; and 4Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan

{dagger}To whom correspondence should be addressed. Tel: +81-44-934-7039, E-mail: shibuya{at}isc.meiji.ac.jp

Received April 20, 2007; Accepted June 29, 2007


  Abstract

Bark lectins from the elderberry plants belonging to the genus Sambucus specifically bind to Neu5Ac{alpha}2,6Gal/GalNAc sequence and have long been used for the analysis of sialoglycoconjugates that play important roles in many biological phenomena. However, molecular basis of such a unique carbohydrate binding specificity has not been understood. To answer these questions, we tried to identify the amino-acid residues in the Japanese elderberry bark lectin, Sambucus sieboldiana agglutinin that enabled the lectin to recognize sialic acid by using in silico docking simulation and site-directed mutagenesis. These studies showed that three amino-acid residues, S197, A233 and Q234, in the C-terminal subdomain of SSA-B chain are critical for the binding to the sialic acid in Neu5Ac{alpha}2,6Gal/GalNAc sequence. Replacement of one of these residues to the one in the corresponding position of ricin B-chain completely abolished the binding to a sialoglycoprotein, fetuin. Conserved presence of these amino acid residues in the corresponding sequences of two other elderberry lectins with similar binding specificity further supported the conclusion. These findings indicated that the replacement of the corresponding amino-acid residues in a putative Gal/GalNAc-specific ancestral lectin to these amino-acid residues generated the unique Neu5Ac{alpha}2,6Gal/GalNAc-specific elderberry lectins in the course of molecular evolution.

Key Words: docking simulation, elderberry, lectin, Sambucus sieboldiana, sialic acid

Abbreviations: PBS, phosphate buffered saline; PDB, protein data bank; RIP, ribosome-inactivating protein; SNA, Sambucus nigra agglutinin; SSA, Sambucus sieboldiana agglutinin

*The first three authors contributed equally to this work.


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