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Topological analysis of the Electron Localisation Function (ELF) within the framework of Quantum Chemical Topology (QCT) has been applied to study the nature of the boron–oxygen bonds. A series of 16 compounds has been chosen, with the experimental B O bond length in the range of 1.481 Å (B O)–1.179 Å (B O). Topological results obtained for the DFT(M062X), DFT(B3LYP), MP2 and CCSD(T) optimised geometrical structures show that all the boron–oxygen bonds in the investigated compounds are described by the disynaptic bonding basin, V(B,O). All these bonds have a covalent-polarised character. The mean electron population of V(B,O) varies from 1.6e (B(OH) 4 − ) to about 3.5e (HN CH CH CH NH B O). The polarity index values, p BO, lie between 0.77 (ClBO) and 0.89 (H 2 BOCH 3 ), thus all boron–oxygen bonds are essentially polarised by the oxygen atom. According to the Lewis formula, four types of the bonds have been recognised. These are: a single bond with a mixture of the ionic hybrid (B O, B + O − ), a single bond (B O), a single bond with a small contribution of the dative O→B bond (B O) and a single bond with a large contribution of the dative O→B bond (depleted B O bonds). There is a clear distinction between a group of 11 molecules chosen for this study, with the basin population value of the boron–oxygen bond between 1.6e and 2.4e, and the HB O, FB O, ClB O, HN CH CH CH NH B O and trans-[(Me3P)2BrPt(B O)] molecules that exhibit the basin population in the range: 3.3e–3.5e. The second group was postulated to have a triple bond, B O, but this statement has not been confirmed by our research. [ABSTRACT FROM AUTHOR]

Abstract: The Arabidopsis thaliana genome contains a small group of bipartite F-box proteins, consisting of an N-terminal F-box domain and a C-terminal domain sharing sequence similarity with Nictaba, the jasmonate-induced glycan-binding protein (lectin) from tobacco. Based on the high sequence similarity between the C-terminal domain of these proteins and Nictaba, the hypothesis was put forward that the so-called F-box-Nictaba proteins possess carbohydrate-binding activity and accordingly can be considered functional homologs of the mammalian sugar-binding F-box or Fbs proteins which are involved in proteasomal degradation of glycoproteins. To obtain experimental evidence for the carbohydrate-binding activity and specificity of the A. thaliana F-box-Nictaba proteins, both the complete F-box-Nictaba sequence of one selected Arabidopsis F-box protein (in casu At2g02360) as well as the Nictaba-like domain only were expressed in Pichia pastoris and analyzed by affinity chromatography, agglutination assays and glycan micro-array binding assays. These results demonstrated that the C-terminal Nictaba-like domain provides the F-box-protein with a carbohydrate-binding activity that is specifically directed against N- and O-glycans containing N-acetyllactosamine (Galβ1-3GlcNAc and Galβ1-4GlcNAc) and poly-N-acetyllactosamine ([Galβ1-4GlcNAc]n) as well as Lewis A (Galβ1-3(Fucα1-4)GlcNAc), Lewis X (Galβ1-4(Fucα1-3)GlcNAc, Lewis Y (Fucα1-2Galβ1-4(Fucα1-3)GlcNAc) and blood type B (Galα1-3(Fucα1-2)Galβ1-3GlcNAc) motifs. Based on these findings one can reasonably conclude that at least the A. thaliana F-box-Nictaba protein encoded by At2g02360 can act as a carbohydrate-binding protein. The results from the glycan array assays revealed differences in sugar-binding specificity between the F-box protein and Nictaba, indicating that the same carbohydrate-binding motif can accommodate unrelated oligosaccharides. [Copyright &y& Elsevier]

The Arabidopsis thaliana genome contains a small group of bipartite F‐box proteins, consisting of an N‐terminal F‐box domain and a C‐terminal domain sharing sequence similarity with Nictaba, the jasmonate‐induced glycan‐binding protein (lectin) from tobacco. Based on the high sequence similarity between the C‐terminal domain of these proteins and Nictaba, the hypothesis was put forward that the so‐called F‐box‐Nictaba proteins possess carbohydrate‐binding activity and accordingly can be considered functional homologs of the mammalian sugar‐binding F‐box or Fbs proteins which are involved in proteasomal degradation of glycoproteins. To obtain experimental evidence for the carbohydrate‐binding activity and specificity of the A. thaliana F‐box‐Nictaba proteins, both the complete F‐box‐Nictaba sequence of one selected Arabidopsis F‐box protein (in casu At2g02360) as well as the Nictaba‐like domain only were expressed in Pichia pastoris and analyzed by affinity chromatography, agglutination assays and glycan micro‐array binding assays. These results demonstrated that the C‐terminal Nictaba‐like domain provides the F‐box‐protein with a carbohydrate‐binding activity that is specifically directed against N‐ and O‐glycans containing N‐acetyllactosamine (Galβ1‐3GlcNAc and Galβ1‐4GlcNAc) and poly‐N‐acetyllactosamine ([Galβ1‐4GlcNAc]n) as well as Lewis A (Galβ1‐3(Fucα1‐4)GlcNAc), Lewis X (Galβ1‐4(Fucα1‐3)GlcNAc, Lewis Y (Fucα1‐2Galβ1‐4(Fucα1‐3)GlcNAc) and blood type B (Galα1‐3(Fucα1‐2)Galβ1‐3GlcNAc) motifs. Based on these findings one can reasonably conclude that at least the A. thaliana F‐box‐Nictaba protein encoded by At2g02360 can act as a carbohydrate‐binding protein. The results from the glycan array assays revealed differences in sugar‐binding specificity between the F‐box protein and Nictaba, indicating that the same carbohydrate‐binding motif can accommodate unrelated oligosaccharides. [ABSTRACT FROM AUTHOR]