Complete primary structure of a newly characterized galactose-specific lectin from the seeds of Dolichos lablab Nagender Rao Rameshwaram & Narasimha Kumar Karanam & Christian Scharf & Uwe Völker & Siva Kumar Nadimpalli Received: 30 May 2008 / Revised: 24 July 2008 / Accepted: 28 July 2008 / Published online: 12 September 2008 # Springer Science + Business Media, LLC 2008 Abstract A new unique lectin (galactose-specific) purified from the seeds of Dolichos lablab, designated as DLL-II is a heterodimer composed of closely related subunits α and β. These were separated by SDS-PAGE and isolated by electroelution. By ESI-MS analysis their molecular masses were found to be 30.746 kDa (α) and 28.815 kDa (β) respectively. Both subunits were glycosylated and displayed similar amino acid composition. Using advanced mass spectrometry in combination with de novo sequencing and database searches for the peptides derived by enzymatic and chemical cleavage of these subunits, the primary sequence was deduced. This revealed DLL-II to be made of two polypeptide chains of 281(α) and 263(β) amino acids respectively. The β subunit differed from the α subunit by the absence of some amino acids at the carboxy terminal end. This structural difference suggests that possibly, the β subunit is derived from the α subunit by posttranslational proteolytic modification at the COOH-terminus. Comparison of the DLL-II sequence to other leguminous seed lectins indicates a high degree of structural conservation. Keywords Dolichos lablab . Leguminosae . Agglutinin . α and β subunits . Matrix-assisted laser desorption/ionisation mass spectrometry . Galactose-specific seed lectin (DLL-II) . Amino acid sequence Abbreviations DLL Dolichos lablab plant DLL- I Glucose/mannose-specific lectin from the seeds of Dolichos lablab DLL- II Galactose-specific lectin from the seeds of Dolichos lablab DLL- VL Galactose-specific lectin from the vegetative tissues of Dolichos lablab MALDI Matrix assisted laser desorption/ionization ESI Electro spray ionisation MS Mass Spectrometry Introduction Boyd and Shapleigh [1] in 1954 coined the term “lectin” for a class of structurally diverse proteins that bind carbohy- drates. Each lectin molecule typically contains two or more binding sites, that is, they are divalent or polyvalent. Therefore, when they react with cells, they will not only combine with sugars on their surfaces but will also cause cross-linking of the cells and their subsequent precipitation, a phenomenon referred to as cell agglutination or hemagglu- tination [2]. A large number of legume lectins characterized have been shown to be oligomers composed of two types of Glycoconj J (2009) 26:161–172 DOI 10.1007/s10719-008-9173-1 Electronic Supplementary Material The online version of this article (doi:10.1007/s10719-008-9173-1) contains supplementary material, which is available to authorized users. N. R. Rameshwaram : S. K. Nadimpalli (*) Department of Biochemistry, School of Life sciences, University of Hyderabad, Hyderabad 500 046, India e-mail: drnsk7@yahoo.co.in N. K. Karanam : C. Scharf : U. Völker Interfaculty Institute for Genetics and Functional Genomics, Ernst-Moritz-Arndt-University Greifswald, Friedrich-Ludwig-Jahn-Str. 15A, 17487 Greifswald, Germany C. Scharf Department of Otorhinolaryngology Head and Neck Surgery, Ernst-Moritz-Arndt-University Greifswald, Walther-Rathenau-Str. 43–45, 17475 Greifswald, Germany