N-acetylglucosamine-phosphatidylinositol de-N-acetylase as a novel target for probing potential inhibitor against Leishmania donovani.

Leishmania donavani is the causative agent of leishmaniasis, responsible for social and economic disruption, especially in developing countries. Lack of effective drugs with few side effects have necessitated the discovery of newer therapeutic solutions for leishmaniasis. Glycophosphatidylinositol (GPI) synthesis plays a vital role in protozoan cell membranes structural formation and antigenic modification. Hence, any disruption in its biosynthesis can prove fatal to the parasitic protozoans. N-acetylglucosamine-phosphatidylinositol de-N-acetylase (NAGP-deacetylase) is an enzyme from the GPI biosynthetic pathway that catalyzes the deacetylation of N-acetylglucosaminylphosphatidylinositol to glucosaminylphosphatidylinositol, a step essential for the proper functioning of the enzyme. In the quest for novel scaffolds as anti-leishmaniasis agents, we have executed in silico virtual screening, density function theory, molecular dynamics and MM-GBSA based energy calculations with a natural product library and a diverse library set from Chembridge database. Two compounds, 14671 and 4610, were identified at the enzyme's active site and interacted with catalytic residues, Asp43, Asp44, His41, His147, His 150, Arg80 and Arg231. Both molecules exhibited stable conformation in their protein-ligand complexes with binding free energies for compound-14671 and compound-4610 of -54 ± 4 and -50 ± 4 kcal/mol, respectively. These scaffolds can be incorporated in future synthetic determinations, focusing on developing druggable inhibitor support, increasing potency, and introducing species selectivity.Communicated by Ramaswamy H. Sarma.

Effects of cell surface α2-3 sialic acid on osteogenesis.

A cell culture model of osteoblast differentiation was applied in our study of the effect of sialic acid on the osteogenesis by using the pre-osteoblast of MC3T3-E1 subclone 14 cells. Following the treatment of different concentrations of α2,3-neuraminidase, which specifically removed the α2-3 sialic acid from cell surface, a significant decrease of α2-3 sialic acid was detected with fluorescein isothiocyanate (FITC)-labeled Maackia amurensis lectin (MAL-II) by flow cytometry analysis. von Kossa staining showed that the bone mineralization decreased in MC3T3-E1 subclone 14 cells after the treatment of α2,3-neuraminidase for 2 weeks. However α2,3-neuraminidase did not affect the formation of osteoblasts in MC3T3-E1 subclone 14 cells, which was demonstrated by positive alkaline phosphatase (ALP)-staining. Characteristic biological markers and osteoblast-like cell-related factors of osteoblastic cells were also examined. Both RT-PCR and Western blot analysis demonstrated that the expression of bone sialoprotein (BSP), osteoprotegerin (OPG), and vitamin D receptor (VDR) were significantly decreased when α2-3 sialic acid expression decreased on the cell surface, while the expression of osteocalcin (OC) and osteopontin (OPN) remained unchanged. We propose a hypothesis that α2-3 sialic acid affects bone mineralization but not osteogenic differentiation.

Bovine coronavirus uses N-acetyl-9-O-acetylneuraminic acid as a receptor determinant to initiate the infection of cultured cells.

The importance of N-acetyl-9-O-acetylneuraminic acid (Neu5,9Ac2) as a receptor determinant for bovine coronavirus (BCV) on cultured cells was analysed. Pretreatment of MDCK I (Madin Darby canine kidney) cells with neuraminidase or acetylesterase rendered the cells resistant to infection by BCV. The receptors on a human (CaCo-2) and a porcine (LLC-PK1) epithelial cell line were also found to be sensitive to neuraminidase treatment. The susceptibility to infection by BCV was restored after resialylation of asialo-MDCK I cells with Neu5,9Ac2. Transfer of sialic acid lacking a 9-O-acetyl group was ineffective in this respect. These results demonstrate that 9-O-acetylated sialic acid is used as a receptor determinant by BCV to infect cultured cells. The possibility is discussed that the initiation of a BCV infection involves the recognition of different types of receptors, a first receptor for primary attachment and a second receptor to mediate the fusion between the viral envelope and the cellular membrane.

[Acquired B antigen]. / L'antigène B acquis

Many cases of acquired B antigens, always observed in group A subjects have been so far reported. Most of them were found in patients with digestive tract disease, essentially colonic cancer. An investigation on 200 patients in a gastroenterology department showed that this B-like antigen was quite frequent (10,6%); it occurred only in A1 individuals and was related to infectious syndrome. Immunological and serological studies of many cases had shown that this B-like antigen differs from that of normal B cells. Groupe A1 cells transfused to patients acquired B activity; on the contrary group A2 and O cells remained unchanged. Likewise, only A1 cell became active when incubated in vitro with C. Tertium A., known to contain a deacetylase. In 1970, we postulated that a deacetylase enzyme could be responsible for this B-like antigen: this enzyme could transform the N-acetylgalactosamine (A specific sugar) into galactosamine, which could cross react with anti-B sera. The relationship between the acquired B antigen and a deacetylase was recently confirmed: A1 acquired B cells, chemically acetylated lost their B reactivity and enhanced their A1 activity. A polyagglutinability, different from that associated with T, Tn, Cad, Hempas has been always found in acquired B cells; nervertheless, because of its weakness, it could sometimes be unnoticed. Besides, it disappeared prior to B reactivity in case of recovery. Like acquired B activity, it decreased in low pH medium of after acetylation of the cells. Nevertheless, this polyagglutinability appears, contrarly to acquired B antigen, in vitro, on all the cells, irrespective of their ABO phenotypes. A deacetylation of N-acetyl-neruaminic acid could explain such a phenomenon.