No abstract

Highlights► Mnt5 adds the second residues of lateral branches of the N-linked mannan outer chain. ► Mnt1 and Mnt2 participate in the addition of the 4° and 5° residues of O-linked mannan. ► Candida albicansO-linked mannans can be extended further than five mannose residues.

We previously demonstrated that, in the early stages of tau processing in Alzheimer's disease, the N-terminal part of the molecule undergoes a characteristic cascade of phosphorylation and progressive misfolding of the proteins resulting in a structural conformation detected by Alz-50. In this immunohistochemical study of AD brain tissue, we have found that C-terminal truncation of tau at Asp-421 was an early event in tau aggregation and analyzed the relationship between phospho-dependent tau epitopes located at the C-terminus with truncation at Glu-391. The aim of this study was to determine whether C-terminal truncation may trigger events leading to the assembly of insoluble PHFs from soluble tau aggregates present in pre-tangle cells. Our findings suggest that there is a complex interaction between phosphorylated and truncated tau species. A model is presented here in which truncated tau protein represents an early neurotoxic species while phosphorylated tau species may provide a neuroprotective role in Alzheimer's disease.

Candida albicans is an opportunistic fungus that is part of the normal microflora commonly found in the human digestive tract and the normal mucosa or skin of healthy individuals. However, in immunocompromised individuals, it becomes a serious health concern and a threat to their lives and is ranked as the leading fungal infection in humans worldwide. As existing treatments for this infection are non-specific or under threat of developing resistance, there is a dire necessity to find new targets for designing specific drugs to defeat this fungus. Some authors reported the presence of the transglutaminase activity in Candida and Saccharomyces, but its identity remains unknown. We report here the phenotypic effects produced by the inhibition of transglutaminase enzymatic activity with cystamine, including growth inhibition of yeast cells, induction of autophagy in response to damage caused by cystamine, alteration of the normal yeast division pattern, changes in cell wall, and inhibition of the yeast-to-mycelium transition. The latter phenomenon was also observed in the C. albicans ATCC 26555 strain. Growth inhibition by cystamine was also determined in other Candida strains, demonstrating the importance of transglutaminase in these species. Finally, we identified enolase 1 as the cell wall protein responsible for TGase activity. After studying the inhibition of enzymatic activities with anti-CaEno1 antibodies and through bioinformatics studies, we suggest that the enolase and transglutaminase catalytic sites are localized in different domains of the protein. The aforementioned data indicate that TGase/Eno1 is a putative target for designing new drugs to control C. albicans infection.

The multidrug resistance (MDR) phenotype inEntamoeba histolytica, the protozoan parasite responsible for human amoebiasis, presents the multidrug resistance (MDR) 1 phenotype (1) described first in mammalian cells (2) and then in several protozoan parasites (3, 4). MDR is associated with the overexpression of a 170-kDa membrane molecule known as P-glycoprotein (PGP), an energy-dependent pump that extrudes drugs from the cells (5, 6). In E. histolytica, MDR phenotype is given mainly by overexpression of the EhPgp1 and EhPgp5 genes, which are finely regulated by transcriptional factors (7-9). Although EhPgp1 is constitutively expressed in drug-resistant trophozoites of clone C2, EhPgp5 gene is overexpressed only when C2 cells are grown in a high emetine concentration (10, 11). Both genes are also amplified in the presence of a high drug concentration (12).Transcriptional regulation of eukaryotic mdr genes has been considered as the major control point for PGP synthesis, although gene amplification mechanisms also participate in this event (12, 13). Moreover, there is growing evidence of pivotal post-transcriptional (14 -17) and post-translational (18 -20) regulation of the PGP expression. On the other hand, mRNA stability has recently emerged as a critical control step in determining cellular stationary mRNA levels. The abundance of a particular mRNA can fluctuate many folds due to alterations in mRNA stability without any change in the transcription rate (21). The mRNA half-life is determined by a complex set of protein interactions at the 3Ј-untranslated region (3Ј-UTR) depending on conserved cis-element sequences and secondary structures (for review, see Ref. 22). The 3Ј-UTR also contains consensus sequence elements that mediate mRNA nuclear export, cytoplasmic localization, translation efficacy, and polyadenylation control (23, 24). The pre-mRNAs are polyadenylated in a reaction involving 3Ј endonucleolytic cleavage followed by poly(A) tail synthesis (25). Poly(A) tail is also a modulator of mRNA stability and translation (26,27). Strict control of poly(A) tail length is achieved by the concerted interplay of key factors, including poly(A) polymerase, deadenylases, and poly(A)-binding protein activities (25).Several reports have addressed the importance of mRNA stability on the mdr genes expression regulation. Pgp1, Pgp2, and Pgp3 mRNAs have a higher half-life in rat tumor cells than in normal cells (15), whereas rat MDR hepatocytes in culture present a higher amount of PGP2 protein due to a post-transcriptional mechanism controlling mRNA stability (14). Human MDR1 mRNA has a half-life of 30 min, which is prolonged to more than 20 h upon treatment with cycloheximide, suggesting that protein synthesis inhibition may influence the stability of certain mRNAs (16,17). However, molecular mechanisms controlling mdr mRNA stability remains to be elucidated.In E. histolytica, mRNA stability mechanisms have not been studied yet. The presence of higher levels of EhPGP5 protein in the multidrug-resistant trophozoites of c...