title: Substrate-bound crystal structures reveal features unique to Mycobacterium tuberculosis N-acetyl-glucosamine 1-phosphate uridyltransferase and a catalytic mechanism for acetyl transfer.
abstract: N-acetyl-glucosamine-1-phosphate uridyltransferase (GlmU), a bifunctional enzyme involved in bacterial cell wall synthesis is exclusive to prokaryotes. GlmU, now recognized as a promising target to develop new antibacterial drugs, catalyzes two key reactions: acetyl transfer and uridyl transfer at two independent domains. Hitherto, we identified GlmU from Mycobacterium tuberculosis (GlmU(Mtb)) to be unique in possessing a 30-residue extension at the C terminus. Here, we present the crystal structures of GlmU(Mtb) in complex with substrates/products bound at the acetyltransferase active site. Analysis of these and mutational data, allow us to infer a catalytic mechanism operative in GlmU(Mtb). In this S(N)2 reaction, His-374 and Asn-397 act as catalytic residues by enhancing the nucleophilicity of the attacking amino group of glucosamine 1-phosphate. Ser-416 and Trp-460 provide important interactions for substrate binding. A short helix at the C-terminal extension uniquely found in mycobacterial GlmU provides the highly conserved Trp-460 for substrate binding. Importantly, the structures reveal an uncommon mode of acetyl-CoA binding in GlmU(Mtb); we term this the U conformation, which is distinct from the L conformation seen in the available non-mycobacterial GlmU structures. Residues, likely determining U/L conformation, were identified, and their importance was evaluated. In addition, we identified that the primary site for PknB-mediated phosphorylation is Thr-418, near the acetyltransferase active site. Down-regulation of acetyltransferase activity upon Thr-418 phosphorylation is rationalized by the structures presented here. Overall, this work provides an insight into substrate recognition, catalytic mechanism for acetyl transfer, and features unique to GlmU(Mtb), which may be exploited for the development of inhibitors specific to GlmU.
authors.affiliation: Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India.
authors.forename: Pravin Kumar Ankush
authors.initials: PK
authors.lastname: Jagtap
authors.forename: Vijay
authors.initials: V
authors.lastname: Soni
authors.forename: Neha
authors.initials: N
authors.lastname: Vithani
authors.forename: Gagan Deep
authors.initials: GD
authors.lastname: Jhingan
authors.forename: Vaibhav Singh
authors.initials: VS
authors.lastname: Bais
authors.forename: Vinay Kumar
authors.initials: VK
authors.lastname: Nandicoori
authors.forename: Balaji
authors.initials: B
authors.lastname: Prakash
mesh_terms: D000105:Acetyl Coenzyme A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000123:Acetyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002384:Catalysis; D018360:Crystallography, X-Ray; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000201:enzymology* / Q000235:genetics; D010766:Phosphorylation / Q000502:physiology; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; C532100:GlmU protein, Mycobacterium tuberculosis; D009097:Multienzyme Complexes; D000105:Acetyl Coenzyme A; D000123:Acetyltransferases