TWO MAIN DOMAINS WITH DIFFERENT ROLES DISCOVERED IN A NEW TOMATO BETA-GALACTOSIDASE

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Agricultural Biotechnology Department, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran

Received December 10, 2015; in final form, April 1, 2016

DOI: 10.7868/S0132342316050067

β-Galactosidases (β-gals) are a wide family of glycosyl hydrolases thought to be involved in the metabolic recycling of galactolipids, glycoproteins, and cell wall polysaccharides in plants. A full-length cDNA, designated STBG2, was isolated and cloned from tomato (Solanum lycopersicum L. cv. Falcato) by reverse transcription–polymerase chain reaction. The cDNA was 2996 bp in length and encoded a typical β-gal protein, designated SlGal2, consisting of 892 residues. A comparison of SlGal2 with its counterpart isoform in the cultivar Rutgers revealed that SlGal2 had identical residues, except for 44 amino acids. Noteworthy, 42 different residues were located in a limited area in the middle of the protein. An alignment of SlGal2 with other plant β-gals clearly showed the existence of a non-conserved short polypeptide, as a connector between the N- and C-terminal domains. A deeper bioinformatic analysis referring to recent experimental findings strongly suggested different roles for the N- and C-terminal domains. As a result, the N-terminal domain is responsible for the catalytic activity and the C-terminal domain is responsible for the stability and the substrate binding of the enzyme. In addition, a substantial difference in physiochemical characteristics of similar β-gals was found to be in their isoelectric points. In conclusion, the differential role of C-terminal domains and also the significant differences in isoelectric points provided insights into the unknown mechanism of substrate specificity of plant β-gals, which in turn will help in protein engineering studies.

Keywords: RT-PCR, lectin, protein, function, sequence annotation.

Биоорг. химия 2016, 42 (5): 578-587