Search

Members of the metallo-ß-lactamase (MBL) superfamily of enzymes harbor a highly conserved aßßa MBL-fold domain and were first described as inactivators of common ß-lactam antibiotics. In humans, these enzymes have been shown to exhibit diverse functions, including hydrolase activity toward amides, esters, and thioesters. An uncharacterized member of the human MBL family, MBLAC2, was detected in multiple palmitoylproteomes, identified as a zDHHC20 S-acyltransferase interactor, and annotated as a potential thioesterase. In this study, we confirmed that MBLAC2 is palmitoylated and identified the likely S-palmitoylation site as Cys254. S-palmitoylation of MBLAC2 is increased in cells when expressed with zDHHC20, and MBLAC2 is a substrate for purified zDHHC20 in vitro. To determine its biochemical function, we tested the ability of MBLAC2 to hydrolyze a variety of small molecules and acylprotein substrates. MBLAC2 has acyl-CoA thioesterase activity with kinetic parameters and acyl-CoA selectivity comparable with acyl-CoA thioesterase 1 (ACOT1). Two predicted zinc-binding residues, Asp87 and His88, are required for MBLAC2 hydrolase activity. Consistent with a role in fatty acid metabolism in cells, MBLAC2 was cross-linked to a photoactivatable fatty acid in a manner that was independent of its S-fatty acylation at Cys254. Our study adds to previous investigations demonstrating the versatility of the MBL-fold domain in supporting a variety of enzymatic reactions. [ABSTRACT FROM AUTHOR]

In the transplant community, research efforts exploring endogenous alternatives to inducing tolerogenic allo-specific immune responses are much needed. In this regard, CD4  +  FoxP3 + regulatory T cells (T regs ) are appealing candidates due to their intrinsic natural immunosuppressive qualities. To date, various homeostatic factors that dictate T reg survival and fitness have been elucidated, particularly the non-redundant roles of antigenic CD3 ζ /T-cell-receptor, co-stimulatory CD28, and cytokine interleukin (IL-)2 dependent signaling. Many of the additional biological signals that affect T regs remain to be elucidated, however, especially in the transplant context. Previously, we demonstrated an unexpected link between type I interferons (IFNs) and T regs in models of multiple myeloma (MM)-where MM plasmacytes escaped immunological surveillance by enhancing type I IFN signaling and precipitating upregulated T reg responses that could be overturned with specific knockdown of type I IFN signaling. Here, we elaborated on these findings by assessing the role of type I IFN signaling (IFN-α and -β) on T reg homeostasis within an alloimmune context. Specifically, we studied the induction of T regs from naïve CD4 T cells. Using in vitro and in vivo models of murine skin allotransplantation, we found that type I IFN indeed spatiotemporally enhanced the polarization of naïve CD4 T cells into FoxP3 + T regs . Notably, however, this effect was not independent of, and rather co-dependent on, ancillary cytokine signals including IL-2. These findings provide evidence for the relevance of type I IFN pathway in modulating FoxP3 + T reg responses and, by extension, stipulate an additional means of facilitating T reg fitness via type I IFNs., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Eskandari, Allos, Safadi, Sulkaj, Sanders, Cravedi, Ghobrial, Berger and Azzi.)