Shape-function insights into bifunctional O-GlcNActransferase of Listeria monocytogenes EGD-e

In Vitro Characterization of an O-Specific Glycosyltransferase Involved in Flagellin Glycosylation

Glycosyltransferases play a fundamental role in the biosynthesis of glycoproteins and glycotherapeutics. In this study, we investigated protein glycosyltransferase FlgGT1, belonging to the GT2 family. The GT2 family includes cysteine S-glycosyltransferases involved in antimicrobial peptide biosyntheses, sharing conserved catalytic domains while exhibiting diverse C-terminal domains. Our in vitro studies revealed that FlgGT1 recognizes structural motifs rather than specific amino acid sequences when glycosylating the flagellin protein Hag. Notably, FlgGT1 is selective for serine or threonine O-glycosylation over cysteine S-glycosylation. Molecular dynamics simulations provided insights into the structural basis of FlgGT1's ability to accommodate various sugar nucleotides as donor substrates. Mutagenesis experiments on FlgGT1 demonstrated that truncating the relatively large C-terminal domain resulted in a loss of flagellin glycosylation activity. Our classification based on sequence similarity network analysis and AlphaFold2 structural predictions suggests that the acquisition of the C-terminal domain is a key evolutionary adaptation conferring distinct substrate specificities on glycosyltransferases within the GT2 family.

Global shape of SvGT, a metal-dependent bacteriocin modifying S/O-HexNActransferase from actinobacteria: c -terminal dimerization modulates the function of this GT

Here, we describe hitherto unknown shape-function of S/O-HexNActransferase SvGT (ORF AQF52_3101) instrumental in glycosylation of bacteriocin SvC (ORF AQF52_3099) in Streptomyces venezuelae ATCC 15439. Data from gel filtration, mass spectrometry, analytical ultracentrifugation, and Small Angle X-ray Scattering (SAXS), experiments confirmed elongated dimeric shape in solution for SvGT protein. Enzyme assays confirmed the dependence of SvGT on the availability of Mg2+ ions to be functionally activated. SAXS data analysis provided that apo and Mg2+-activated protein adopt a shape characterized by a radius of gyration and maximum linear dimension of 5.2 and 17.0 nm, and 5.3 and 17.8 nm, respectively. Alphafold2 server was used to model the monomeric chain of this protein which was docked on self to obtain different poses of the dimeric entity. Experimental SAXS data was used to select and refine the structure of SvGT dimer. Results showed that Mg2+ ions induce reorientation of the GT domain of one chain leading to a dimer with C2 symmetry, and the C-terminal portion entangles with each other in all states. Mutation-rendered alteration in activity profiles confirmed the role of conserved residues around catalytic motif. Global structure analysis puts forth the need to understand the role of constitutionally diverse C-terminal portion in regulating substrate selectivity.Communicated by Ramaswamy H. Sarma.

Structural basis of flagellar motility regulation by the MogR repressor and the GmaR antirepressor in Listeria monocytogenes

The pathogenic Listeria monocytogenes bacterium produces the flagellum as a locomotive organelle at or below 30°C outside the host, but it halts flagellar expression at 37°C inside the human host to evade the flagellum-induced immune response. Listeria monocytogenes GmaR is a thermosensor protein that coordinates flagellar expression by binding the master transcriptional repressor of flagellar genes (MogR) in a temperature-responsive manner. To understand the regulatory mechanism whereby GmaR exerts the antirepression activity on flagellar expression, we performed structural and mutational analyses of the GmaR-MogR system. At or below 30°C, GmaR exists as a functional monomer and forms a circularly enclosed multidomain structure via an interdomain interaction. GmaR in this conformation recognizes MogR using the C-terminal antirepressor domain in a unique dual binding mode and mediates the antirepressor function through direct competition and spatial restraint mechanisms. Surprisingly, at 37°C, GmaR rapidly forms autologous aggregates that are deficient in MogR neutralization capabilities.

Demystifying the O-GlcNAc Code: A Systems View

Post-translational modification with O-linked β-N-acetylglucosamine (O-GlcNAc), a process referred to as O-GlcNAcylation, occurs on a vast variety of proteins. Mounting evidence in the past several decades has clearly demonstrated that O-GlcNAcylation is a unique and ubiquitous modification. Reminiscent of a code, protein O-GlcNAcylation functions as a crucial regulator of nearly all cellular processes studied. The primary aim of this review is to summarize the developments in our understanding of myriad protein substrates modified by O-GlcNAcylation from a systems perspective. Specifically, we provide a comprehensive survey of O-GlcNAcylation in multiple species studied, including eukaryotes (e.g., protists, fungi, plants, Caenorhabditis elegans, Drosophila melanogaster, murine, and human), prokaryotes, and some viruses. We evaluate features (e.g., structural properties and sequence motifs) of O-GlcNAc modification on proteins across species. Given that O-GlcNAcylation functions in a species-, tissue-/cell-, protein-, and site-specific manner, we discuss the functional roles of O-GlcNAcylation on human proteins. We focus particularly on several classes of relatively well-characterized human proteins (including transcription factors, protein kinases, protein phosphatases, and E3 ubiquitin-ligases), with representative O-GlcNAc site-specific functions presented. We hope the systems view of the great endeavor in the past 35 years will help demystify the O-GlcNAc code and lead to more fascinating studies in the years to come.