Sequence, Structure, and Binding Site Analysis of Kirkiin in Comparison with Ricin and Other Type 2 RIPs

• Published in: Toxins Vol. 13; no. 12; p. 862
• Main Authors: Maiello, Stefania, Iglesias, Rosario, Polito, Letizia, Citores, Lucía, Bortolotti, Massimo, Ferreras, José M, Bolognesi, Andrea
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 03-12-2021; MDPI
• Subjects: 3D structure; Affinity; Amino Acid Sequence; Amino acids; Apoptosis; Binding Sites; Biotechnology; Catalytic Domain; Chains; Cytotoxicity; D-Galactose; Galactose; Introns; kirkiin; Lactose; Molecular Docking Simulation; Passifloraceae - chemistry; Passifloraceae - genetics; Plant Proteins - chemistry; plant toxin; primary sequence; Protein Domains; Protein synthesis; Proteins; Ribosome Inactivating Proteins, Type 2 - chemistry; Ribosome Inactivating Proteins, Type 2 - genetics; Ribosome-inactivating protein; Ricin; Ricin - chemistry; Sequence analysis; Sequence Analysis, DNA; Sugar; Therapeutic applications; Toxicity; cancer therapy; plant toxin; toxic lectin; ricin; kirkiin; ribosome-inactivating protein; 3D structure; primary sequence; sugar specificity
• ISSN: 2072-6651; 2072-6651
• DOI: 10.3390/toxins13120862

Kirkiin is a new type 2 ribosome-inactivating protein (RIP) purified from the caudex of
with a cytotoxicity compared to that of stenodactylin. The high toxicity of RIPs from
genus plants makes them interesting tools for biotechnology and therapeutic applications, particularly in cancer therapy. The complete amino acid sequence and 3D structure prediction of kirkiin are here reported. Gene sequence analysis revealed that kirkiin is encoded by a 1572 bp open reading frame, corresponding to 524 amino acid residues, without introns. The amino acid sequence analysis showed a high degree of identity with other
RIPs. The 3D structure of kirkiin preserves the overall folding of type 2 RIPs. The key amino acids of the active site, described for ricin and other RIPs, are also conserved in the kirkiin A chain. Sugar affinity studies and docking experiments revealed that both the 1α and 2γ sites of the kirkiin B chain exhibit binding activity toward lactose and D-galactose, being lower than ricin. The replacement of His246 in the kirkiin 2γ site instead of Tyr248 in ricin causes a different structure arrangement that could explain the lower sugar affinity of kirkiin with respect to ricin.