GLYCOCINS: The sugar peppered antimicrobials.

Glycosylated bacteriocins, known as glycocins, were first discovered in 2011. These bioactive peptides are produced by bacteria to gain survival advantages. They exhibit diverse types of glycans and demonstrate varied antimicrobial activity. Currently, there are 13 experimentally known glycocins, with over 250 identified in silico across different bacterial phyla. Notably, glycocins are recognized for their glycan-mediated antimicrobial activity, proving effective against drug-resistant and foodborne pathogens. Many glycocins contain rare S-linked glycans. Glycosyltransferases (GTs), responsible for transferring sugar to glycocins and involved in glycocin biosynthesis, often cluster together in the producer's genome. This clustering makes them valuable for custom glycoengineering with diverse substrate specificities. Heterologous expression of glycocins has paved the way for the establishment of microbial factories for glycopeptide and glycoconjugate production across various industries. In this review, we emphasize the primary roles of fully and partially characterized glycocins and their glycosylating enzymes. Additionally, we explore how specific glycan structures facilitate these functions in antibacterial activities. Furthermore, we discuss newer approaches and increasing efforts aimed at exploiting bacterial glycobiology for the development of food preservatives and as replacements or complements to traditional antibiotics, particularly in the face of antibiotic-resistant pathogenic bacteria.

SELECT-GLYCOCIN: a recombinant microbial system for expression and high-throughput screening of glycocins.

Glycosylated bacteriocins (glycocins) are potential clean label food preservatives and new alternatives to antibiotics. Further development requires the availability of a method for laboratory evolution of glycocins, wherein the challenges to overcome include ensuring glycosylation in a heterologous host, avoiding potential toxicity of active glycocins to the host, and provisioning of a one-pot screening assay for active mutants. Employing EntS, a sequential O/S- di-glycosyltransferase from Enterococcus faecalis TX0104, a proof of the concept microbial system and high throughput screening assay (SELECT-GLYCOCIN) is developed for generation of O/S- linked glycopeptide libraries and screening of glycocins for desired activity/property. The method enabled enzyme-dependent in vivo glycosylation in the heterologous host and rapid screening of mutants of enterocin 96 (Ent96)- a glycocin active against food-borne pathogen L. monocytogenes. Using SELECT-GLYCOCIN, a library of random (1.5 X 10^3) and rational (17) mutants of Ent96 was generated. The mutants were screened for bioactivity to identify a total of 376 random and 14 rational mutants as bioactive. Downstream detailed analysis of 16 random and 14 rational mutants led to the identification of sequence- and or glyco-variants namely, G16E-H24Q, C13T, and Ent96-K4_K5insYYGNGV (PedioEnt96) as improved antimicrobials. To summaries, SELECT-GLYCOCIN provides a system and a generic method for discovery and screening of glycocins that can further be adapted to any known/unknown glycocins and can be employed in food preservatives' and drug discovery programs.

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

O-GlcNAcylation is an important post-translational modification of proteins. O-GlcNAcylated proteins have crucial roles in several cellular contexts both in eukaryotes and bacteria. O-GlcNActransferase (OGT) is the enzyme instrumental in O-GlcNAcylation of proteins. OGT is conserved across eukaryotes. The first bacterial OGT discovered is GmaR in Listeria monocytogenes. GmaR is a GT-2 family bifunctional protein that catalyzes glycosylation of the flagellin protein FlaA and controls transcription of flagellar motility genes in a temperature-dependent manner. Here, we provide methods for heterologous expression and purification of recombinant GmaR and FlaA, in vivo/in vitro glycosylation assays, analysis of the molecular form of recombinant GmaR and detailed enzyme kinetics. We study the structure and functional dynamics of GmaR. Using solution small-angle X-ray scattering and molecular modeling, we show that GmaR adopts an extended shape with two distinctly spaced structural units in the presence of cofactor Mg2+ and with donor UDP-GlcNAc and cofactor combined. Comparisons of restored structures revealed that in-solution binding of Mg2+ ions brings about shape rearrangements and induces structural-rigidity in hyper-variable regions at the N-terminus of GmaR protein. Taking function and shape data together, we describe that Mg2+ binding enables GmaR to adopt a shape that can bind the substrate. The manuscript provides the first 3D solution structure of a bacterial OGT of GT-2 family and detailed biochemical characterization of GmaR to facilitate its future applications.

ProGlycProt V2.0, a repository of experimentally validated glycoproteins and protein glycosyltransferases of prokaryotes.

Knowledge of glycosylation status and glycan-pattern of proteins are of considerable medical, academic and application interest. ProGlycProt V2.0 (www.proglycprot.org) therefore, is conceived and maintained as an exclusive web-resource providing comprehensive information on experimentally validated glycoproteins and protein glycosyltransferases (GTs) of prokaryotic origin. The second release of ProGlycProt features a major update with a 191% increase in the total number of entries, manually collected and curated from 607 peer-reviewed publications, on the subject. Protein GTs from prokaryotes that catalyze a varied range of glycan linkages are amenable glycoengineering tools. Therefore, the second release presents content that is greatly expanded and reorganized in two sub-databases: ProGPdb and ProGTdb. While ProGPdb provides information about validated glycoproteins (222 entries), ProGTdb catalogs enzymes/proteins that are instrumental in protein glycosylation, directly (122) or as accessory proteins (182). ProGlycProt V2.0 remains highly cross-referenced yet exclusive and complementary in content to other related databases. The second release further features enhanced search capability, a "compare" entries option and an innovative geoanalytical tool (MapView) facilitating location-assisted search-cum filtering of the entries using geo-positioning information of researchers/groups cited in the ProGlycProt V2.0 databases. Thus, ProGlycProt V2.0 continues to serve as a useful one-point web-resource on various evidence-based information on protein glycosylation in prokaryotes.