Analyzing & Determining the Structure of Penicillin Binding Protein 5 from Enterococcus faeciumtextLee, ChristophercreatorPeti, WolfgangAdvisorSchell, JacquelynReaderMathiowitz, EdithReaderBrown University. Department of Molecular Pharmacology, Physiology and Biotechnologysponsor2017, None p.born digitalThesis (Sc. M.)--Brown University, 2017thesesPenicillin Binding Protein 5 (PBP5) is a membrane bound transpeptidase that plays an important role in β-lactam antibiotic resistance in Enterococcus faecium. Normally, β-lactams inhibit the transpeptidase activity of Penicillin Binding Proteins (PBPs) by way of irreversible acylation of the antibiotic to an active site serine. However, the PBP of E. faecium (PBP5) has been observed to be unaffected by β-lactam inhibition and continues to function as a transpeptidase. Studying this enzyme is important in understanding the steps taken in these unique resistance mechanisms, which can be beneficial in future drug design strategies. Here, we report the crystal structure of PBP5, which displays a highly conserved active site within the C-terminal domain. Through various protein purification techniques and X-ray crystallography, we were able to determine the structure of PBP5 at a resolution of 2.7 Å. We also report the crystal structures of β-lactam acyl-enzyme complexes PBP5:Penicillin G and PBP5:Imipenm, which were solved at a resolution of 2.9 Å and 2.8 Å, respectively. Structural alignment and analysis revealed small structural differences between the PBP5 apo structure and each respective acyl-enzyme complex, displaying the ineffectiveness of antibiotics on PBP5. We also observed similarities between PBP5 and another PBP known as PBP2a of Staphylococcus aureus. PBP2a is also known to be resistant towards β-lactam antibiotics. Superposition of PBP5 and PBP2a revealed a highly conserved active site in both structures as well as similar active site interactions with Penicillin G. This could indicate a resistance mechanism that is shared between both PBPs. Despite a highly conserved active site; sequence and structural alignments denote a high degree of variability between both enzymes. Most notably, the structure of PBP5 reveals no current evidence of an allosteric region within its structure, unlike the reported structure of PBP2a that suggests the presence of an allosteric site. PBPsCrystallographyHigh performance liquid chromatographyEnglishRPB2017061610.7301/Z0S46QDXIn CopyrightCollection is open for research.