page_title: OBPgp279
section_title: Predicted enzyme mechanism
hierarchical_section_title: OBPgp279 / Predicted enzyme mechanism
caption_attribution_description: English: Conserved residues surrounding the catalytic acid, Glu67, in the gycoside hydrolase family 19 papaya chitinase (PDB ID 3cql). A GlcNAc2 unit binding in the -1 and +1 subsites is shown in narrow stick representation and an arrow indicates the position of the glycosidic oxygen.
context_page_description: OBPgp279 is an endolysin that hydrolyzes peptidoglycan, a major constituent in bacterial membrane. OBPgp279 is found in Pseudomonas fluorescens phage OBP, which belongs in the Myoviridae family of bacteriophages. Because of its role in hydrolyzing the peptidoglycan layer, OBPgp279 is a key enzyme in the lytic cycle of the OBP bacteriophage; it allows the bacteriophage to lyse its host internally to escape. Unlike other endolysins, OBPgp279 does not rely on holins to perforate the inner bacterial membrane in order to reach the peptidoglycan layer. Although OBPgp279 is not a well-studied enzyme, it has garnered interest as a potential antibacterial protein due to its activity against multidrug-resistant gram-negative bacteria.
context_section_description: The mechanism of OBPgp279 is predicted to be analogous to glycoside hydrolase family 19 due to the presence of a conserved sequence motif (general sequence motif = [FHY]-G-R-G-[AP]-ζ-Q-[IL]-[ST]-[FHYW]-[HN]-[FY]-[NY], ζ= hydrophilic amino acid) in the catalytic domain of the enzyme. Glycoside hydrolase family 19 is a group of endo-acting enzymes that hydrolyzes the glycosidic bonds of β-1,4-linked N-Acetylglucosamine (GlcNAc) typically within chitin; however, some enzymes in this family also demonstrate lysozyme activity.
  Since bacterial cell walls do not contain chitin, OBPgp279 hydrolyzes β-1,4-linked GlcNAc in peptidoglycan. The hydrolysis of β-1,4-linked GlcNAc is catalyzed by two glutamate residues in the active side, one acting as a general acid, and another acting as a general base.
  There is limited detail on the catalytic mechanism of OBPgp279. However, because OBPgp279 is analogous to family 19, it is possible to infer the structure of OBPgp279 binding to peptidoglycan from the substrate binding of glycoside hydrolase family 19. The figure on the right shows an example of a glycoside hydrolase family 19 binding to chitin. OBPgp279 most likely has a similar active site, but it binds to peptidoglycan instead of chitin.
  Due to the activity of OBPgp279 on β-1,4-linked GlcNAc, it is likely that OBPgp279 is a N-acetylmuramidase (lysozyme-like) endolysin which hydrolyzes the sugar backbone component of the peptidoglycan on the reducing side of GlcNAc.
caption: Active site of gycoside hydrolase family 19 papaya chitinase (PDB: 3cql​).[4] Conserved residues are shown surrounding the catalytic acid, Glu67. A GlcNAc2 unit binding in the -1 and +1 subsites is shown in narrow stick representation and an arrow indicates the position of the glycosidic oxygen.
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