E2-RING Expansion of the NEDD8 Cascade Confers Specificity to Cullin Modification
MOLECULAR CELL
Authors: Huang, Danny T.; Ayrault, Olivier; Hunt, Harold W.; Taherbhoy, Asad M.; Duda, David M.; Scott, Daniel C.; Borg, Laura A.; Neale, Geoffrey; Murray, Peter J.; Roussel, Martine F.; Schulman, Brenda A.
Abstract
Ubiquitin and ubiquitin-like proteins (UBLs) are directed to targets by cascades of El, E2, and E3 enzymes. The largest ubiquitin E3 subclass consists of cullin-RING ligases (CRLs), which contain one each of several cullins (CUL1, -2, -3, -4, or -5) and RING proteins (RBX1 or -2). CRLs are activated by ligation of the UBL NEDD8 to a conserved cullin lysine. How is cullin NEDD8ylation specificity established? Here we report that, like UBE2M (also known as UBC12), the previously uncharacterized E2 UBE2F is a NEDD8-conjugating enzyme in vitro and in vivo. Biochemical and structural analyses indicate how plasticity of hydrophobic E1-E2 interactions and El conformational flexibility allow one El to charge multiple E2s. The E2s; have distinct functions, with UBE2M/RBX1 and UBE2F/RBX2 displaying different target cullin specificities. Together, these studies reveal the molecular basis for and functional importance of hierarchical expansion of the NEDD8 conjugation system in establishing selective CRL activation.
Modulation of host ubiquitin system genes in human endometrial cell line infected with Mycobacterium tuberculosis
MEDICAL MICROBIOLOGY AND IMMUNOLOGY
Authors: Meenu, S.; Thiagarajan, S.; Ramalingam, Sudha; Michael, A.; Ramalingam, Sankaran
Abstract
Endometrium is one of the most commonly affected sites in genital tuberculosis. The understanding of its interaction with the tubercle bacilli is of paramount importance for studying the pathogenesis of this disease. The main objective of this work was to study the interplay between Mycobacterium tuberculosis and host endometrial epithelial cell lines (Ishikawa cell lines), and to identify the differentially expressed genes upon tuberculosis infection. To study this, suppression subtractive hybridization library was constructed using M. tuberculosis H37Rv-infected Ishikawa cell line harvested 24 h post-infection. The subtracted cDNA library was screened, and 105 differentially expressed genes were identified and grouped based on their functions. Since ubiquitination process has gained importance in targeting M. tuberculosis to xenophagy, ubiquitin system genes obtained in the library were selected, and time course analysis of their gene expression was performed. We observed an upregulation of mkrn1 and cops5 and downregulation of zfp91, ndfip2, ube2f, rnft1, psmb6, and psmd13 at 24 h post-infection. From the results obtained, we surmise that ubiquitination pathway genes may have roles in combating tuberculosis which are yet uncharted.