Functional characterization of two members of histidine phosphatase superfamily in Mycobacterium tuberculosis

Metabolic switching and cell wall remodelling of Mycobacterium tuberculosis during bone tuberculosis

OBJECTIVES

Bone tuberculosis (TB) is the third most common types of extrapulmonary tuberculosis. It is critical to understand mycobacterial adaptive strategies within bone lesions to identify mycobacterial factors that may have role in disease pathogenesis.

METHODS

Whole genome microarray was used to characterize the in-vivo transcriptome of Mycobacterium tuberculosis (M.tb) within bone TB specimens. Mycobacterial virulent proteins were identified by bioinformatic software. An in vitro osteoblast cell line model was used to study the role of these proteins in bone TB pathogenesis.

RESULTS

914 mycobacterial genes were significantly overexpressed and 1688 were repressed in bone TB specimens. Pathway analysis of differentially expressed genes demonstrated a non-replicative and hypometabolic state of M.tb, reinforcement of the mycobacterial cell wall and induction of DNA damage repair responses, suggesting possible survival strategies of M.tb within bone. Bioinformatics mining of microarray data led to identification of five virulence proteins. The genes encoding these proteins were also upregulated in the in vitro MC3T3 osteoblast cell line model of bone TB. Further, exposure of osteoblast cells to two of these virulence proteins (Rv1046c and Rv3663c) significantly inhibited osteoblast differentiation.

CONCLUSION

M.tb alters its transcriptome to establish infection in bone by upregulating certain virulence genes which play a key role in disturbing bone homeostasis.

Identification of differentially expressed genes in salt-tolerant oilseed sunflower (Helianthus annuus L.) genotype by RNA sequencing

BACKGROUND

Sunflower (Helianthus annuus L.) is widely planted as an oilseed crop worldwide. Salt stress is one of the major abiotic stresses that negatively affect crop growth and productivity. To counter the negative impact of salt stress, plants have developed avoidance and tolerance mechanisms. Developing salt-tolerant genotypes requires understanding the molecular basis of adaptive mechanisms in depth. Although using model plants i.e., Arabidopsis has improved our understanding of salt tolerant mechanisms, the relative impotence and regulation mechanisms vary among plant species due to differences in genetic and metabolic backgrounds. On the other hand, sunflower is a highly polymorphic plant due to its cross-pollinated behavior which provides different salt-tolerant genotypes available for comparative analyses.

METHODS AND RESULTS

In order to gain a better view of molecular mechanisms involved in salt tolerance in sunflower, RNA sequencing analysis was realized by evaluating a tolerant genotype (AS5305) with two biological replicates under control and salt stress conditions in a controlled environment. Salinity stress was applied from NaCl resource at the 8-leaf stage and samplings were done at 24 h post salt stress application. Sequencing data were analyzed using tuxedo software suite. Blast2GO software and the KEGG database were used to identify the functional tasks of each of the assembled transcripts. Analysis of genes with robust expression (i.e., with FPKM > 1 in at least one sample) revealed a total of 121 significantly expressed genes between the saline-stressed and control samples. The differential expression of 11 genes was confirmed by real-time PCR. In the following, the cDNA of MYB44 as one of the selected candidate genes involved in salt tolerance was isolated, cloned, and sequenced for comparison.

CONCLUSIONS

Overall, the results of the current study may pave the way for the accurate selection of genes involved in salinity to be used in molecular-genetics-assisted breeding programs. In addition, making use of the identified genes may help relieve the damages arising from the salt stress in sunflowers.

Involvement of Leishmania Phosphatases in Parasite Biology and Pathogeny

In the Leishmania lifecycle, the motile promastigote form is transmitted from the sand fly vector to a mammalian host during a blood meal. Inside vertebrate host macrophages, the parasites can differentiate into the amastigote form and multiply, causing leishmaniasis, one of the most significant neglected tropical diseases. Leishmania parasites face different conditions throughout their development inside sand flies. Once in the mammalian host, the parasites have to overcome the microbicide repertoire of the cells of the immune system to successfully establish the infection. In this context, the expression of protein phosphatases is of particular interest. Several members of the serine/threonine-specific protein phosphatase (STP), protein tyrosine phosphatase (PTP), and histidine acid phosphatase (HAcP) families have been described in different Leishmania species. Although their physiological roles have not been fully elucidated, many studies suggest they have an involvement with parasite biology and pathogeny. Phosphatases play a role in adaptation to nutrient starvation during parasite passage through the sand fly midgut. They are also important to parasite virulence, mainly due to the modulation of host cytokine production and impairment of the microbiocidal potential of macrophages. Furthermore, recent whole-genome expression analyses have shown that different phosphatases are upregulated in metacyclic promastigotes, the infective form of the mammalian host. Leishmania phosphatases are also upregulated in drug-resistant strains, probably due to the increase in drug efflux related to the activation of ABC transporters. Throughout this review, we will describe the physiological roles that have been attributed to Leishmania endogenous phosphatases, including their involvement in the adaptation, survival, and proliferation of the parasites inside their hosts.

Structural analysis of EhPSP in complex with 3-phosphoglyceric acid from Entamoeba histolytica reveals a basis for its lack of phosphoglycerate mutase activity

Entamoeba histolytica phosphoserine phosphatase (EhPSP), a regulatory enzyme in the serine biosynthetic pathway, is also a structural homolog of cofactor-dependent phosphoglycerate mutase (dPGM). However, despite sharing many of its catalytic residues with dPGM, EhPSP displays no significant mutase activity. In the current work, we determined a crystal structure of EhPSP in complex with 3-PGA to 2.5 Å resolution and observed striking differences between the orientation of 3-PGA bound to EhPSP and that to its other homologous structures. We also performed computational modeling and simulations of the intermediate 2,3-bisphosphoglyceric acid into the active site of EhPSP to better understand its mechanistic details. Based on these results and those of a similar study with the dPGMs from E. coli and B. pseudomallei, the affinity of EhPSP for 2,3-BPG was concluded to be lower than those of the other proteins. Moreover, a different set of 2,3-BPG interacting residues was observed in EhPSP compared to dPGMs, with all of the crucial interacting residues of dPGMs either missing or substituted with weakly interacting residues. This study has expanded our understanding, at the structural level, of the inability of EhPSP to catalyze the mutase reaction and has strengthened earlier conclusions indicating it to be a true phosphatase.