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J. Biol. Chem., Vol. 282, Issue 15, 11021-11029, April 13, 2007

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Primary Structure and Carbohydrate Binding Specificity of a Potent Anti-HIV Lectin Isolated from the Filamentous Cyanobacterium Oscillatoria agardhii^*

From the Graduate School of Biosphere Science, Hiroshima University, Kagamiyama 1-4-4, Higashi-Hiroshima 739-8528, Japan

The primary structure of a lectin, designated Oscillatoria agardhii agglutinin (OAA), isolated from the freshwater cyanobacterium O. agardhii NIES-204 was determined by the combination of Edman degradation and electron spray ionization-mass spectrometry. OAA is a polypeptide (M_r 13,925) consisting of two tandem repeats. Interestingly, each repeat sequence of OAA showed a high degree of similarity to those of a myxobacterium, Myxococcus xanthus hemagglutinin, and a marine red alga Eucheuma serra lectin. A systematic binding assay with pyridylaminated oligosaccharides revealed that OAA exclusively binds to high mannose (HM)-type N-glycans but not to other N-glycans, including complex types, hybrid types, and the pentasaccharide core or oligosaccharides from glycolipids. OAA did not interact with any of free mono- and oligomannoses that are constituents of the branched oligomannosides. These results suggest that the core disaccharide, GlcNAc-GlcNAc, is also essential for binding to OAA. The binding activity of OAA to HM type N-glycans was dramatically decreased when 1–2 Man was attached to 1–3 Man branched from the 1–6 Man of the pentasaccharide core. This specificity of OAA for HM-type oligosaccharides is distinct from other HM-binding lectins. Kinetic analysis with an HM heptasaccharide revealed that OAA possesses two carbohydrate binding sites per molecule, with an association constant of 2.41x10⁸ M^–1. Furthermore, OAA potently inhibits human immunodeficiency virus replication in MT-4 cells (EC₅₀ = 44.5 nM). Thus, we have found a novel lectin family sharing similar structure and carbohydrate binding specificity among bacteria, cyanobacteria, and marine algae.

Received for publication, February 12, 2007 , and in revised form, February 21, 2007.

^* This work was supported in part by a grant-in-aid for Scientific Research (B) from Japan Society of the Promotion of Science. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The protein sequence data reported in this paper will appear in the Swiss-Prot and TrEMBL knowledge base under the accession numbers P84330 [GenBank] for OAA and P84331 [GenBank] for ESA-2.

¹ Present address: National Research Institute of Brewing, Kagamiyama 3-7-1, Higashi-Hiroshima, Japan.

² To whom correspondence should be addressed. Tel.: 81-82-424-7931; Fax: 81-82-424-7916; E-mail: kanhori{at}hiroshima-u.ac.jp.

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