Two Distinct Jacalin-Related Lectins with a Different Specificity and Subcellular Location Are Major Vegetative Storage Proteins in the Bark of the Black Mulberry Tree

Abstract

Using a combination of protein isolation/characterization and molecular cloning, we have demonstrated that the bark of the black mulberry tree (Morus nigra) accumulates large quantities of a galactose-specific (MornigaG) and a mannose (Man)-specific (MornigaM) jacalin-related lectin. MornigaG resembles jacalin with respect to its molecular structure, specificity, and co-and posttranslational processing indicating that it follows the secretory pathway and eventually accumulates in the vacuolar compartment. In contrast, MornigaM represents a novel type of highly active Man-specific jacalin-related lectin that is synthesized without signal peptide or other vacuolar targeting sequences, and accordingly, accumulates in the cytoplasm. The isolation and cloning, and immunocytochemical localization of MornigaG and MornigaM not only demonstrates that jacalin-related lectins act as vegetative storage proteins in bark, but also allows a detailed comparison of a vacuolar galactose-specific and a cytoplasmic Man-specific jacalin-related lectin from a single species. Moreover, the identification of MornigaM provides the first evidence, to our knowledge, that bark cells accumulate large quantities of a cytoplasmic storage protein. In addition, due to its high activity, abundance, and ease of preparation, MornigaM is of great potential value for practical applications as a tool and bioactive protein in biological and biomedical research.

The Expression Profile of Lectin Differs from That of Seed Storage Proteins inCastanea crenataTrees

“…19) Most woody perennial VSPs have been found in bark and are lectins or lectin-like proteins, but minus lectin activities. 8) Thus far, no detailed study has determined the behavior of VSPs in seeds, because it was assumed that seed storage proteins, such as 7S or 11S globulin, alone function as storage proteins.…”

“…To date, the former has been isolated only in the Moraceae, [6][7][8] while the latter has been widely observed throughout the plant kingdom in, for example, dicots, [8][9][10][11] monocots, 12,13) gymnosperms, 14) and true ferns. 15) Because these lectins recognize foreign glycans and because some are induced by jasmonate, 12) they are assumed to be defense proteins.…”

Glycotope Structures and Intramolecular Affinity Factors of Plant Lectins for Tn/T Antigens

“…Moreover, a comparative analysis indicated that Gleheda and all other previously described Lamiaceae lectins represent a homogeneous subgroup of the legume lectin family. A second interesting novel Tn/T-specific lectin was purified from the bark of the black mulberry tree (Morus nigra, Moraceae) [31] and according to its origin was called Morniga-G (which stands for Morus nigra Gal-specific agglutinin) to distinguishe it from the conspecific mannose-specific homolog Morniga-M [32,33].…”

Two jacalin-related lectins from seeds of the African breadfruit (Treculia africana L.)

“…The reactivities of CRLL, TAA-M, and TAA-G were 100, 37.6 and 18.4%, respectively, suggesting that the two lectins from seeds of T. africana are JRLs. Lim et al 47) reported the contents of two types of JRLs in seeds of two Artocarpus species, and Van Damme et al 9) reported them in bark and seeds of M. nigra. Notes: TAA-G sequence is aligned using CLUSTAL W with other gJRLs, AHL: Artocarpus hirsuta lectin, 41) Frutalin, 42) Jacalin, 43) MPA, 43) Morniga G. 9) Shaded letters denote the residues found in the binding with T-antigen.…”

“…Stacking interactions of the aromatic residues with galactose are important for Jacalin, whilst no aromatic residue is found in the binding site of Artocarpin. Van Damme et al 9) reported that the bark of black mulberry (Morus nigra) contained a plenty of the two kinds of JRLs, Morniga G and Morniga M. Further, it has been known that jackfruit (Artocarpus integrifolia) contains the two kinds of lectins, Jacalin and Artocarpin, 10) in the seeds. As gJRLs, Maclura pomifera agglutinin (MPA), 5,11) Morniga G, 5) and several Artocarpus lectins, [12][13][14][15][16] including Jacalin, have been reported.…”