Structural analysis of the Rhizoctonia solani agglutinin reveals a domain-swapping dimeric assembly

Authors


Correspondence

D. D. Leonidas, Department of Biochemistry and Biotechnology, University of Thessaly, 26 Ploutonos Str., 41221 Larissa, Greece

Fax: +30 2410565290

Tel.: +30 2410565278

E-mail: ddleonidas@bio.uth.gr

E. J. M. Van Damme, Department of Molecular Biotechnology, Ghent University, Coupure Links 653, B-9000, Ghent, Belgium

Fax: +32 92646219

Tel.: +32 92646086

E-mail: elsjm.vandamme@ugent.be

Abstract

Rhizoctonia solani agglutinin (RSA) is a 15.5-kDa lectin accumulated in the mycelium and sclerotia of the soil born plant pathogenic fungus R. solani. Although it is considered to serve as a storage protein and is implicated in fungal insecticidal activity, its physiological role remains unclear as a result of a lack of any structure/function relationship information. Glycan arrays showed that RSA displays high selectivity towards terminal nonreducing N-acetylgalactosamine residues. We determined the amino acid sequence of RSA and also determined the crystal structures of the free form and the RSA–N-acetylgalactosamine complex at 1.6 and 2.2 Å resolution, respectively. RSA is a homodimer comprised of two monomers adopting the β-trefoil fold. Each monomer accommodates two different carbohydrate-binding sites in an asymmetric way. Despite RSA topology similarities with R-type lectins, the two-monomer assembly involves an N-terminal swap, thus creating a dimer association novel to R-type lectins. Structural characterization of the two carbohydrate-binding sites offers insights on the structural determinants of the RSA carbohydrate specificity.

Database

Structural data have been deposited in the Protein Data Bank database under accession numbers 4G9M and 4G9N.

Structured digital abstract

RSA and RSA bind by x-ray crystallography (View interaction)

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