All ETDs from UAB

Advisory Committee Chair

Narayana Sthanam

Advisory Committee Members

Debasish Chattopadhyay

Todd J Green

Aaron L Lucius

David L Littlefield

Document Type

Dissertation

Date of Award

2019

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

A wide range of infections is attributed to the pathogenesis of Gram-positive bacteria. The emergence of multi-drug-resistant Gram-positive pathogens has been a significant health concern and present serious therapeutic challenges globally. Some of the common Gram-positive bacterial species like Streptococcus pneumonia, Group B Streptococcus, and Staphylococcus aureus are infectious by employing several virulence factors for initial adhesion, colonization, biofilm initiation and dispersion, complement evasion, nutrient acquisition, and infection. The structural insights into these virulence factors are essential for understanding their mode of action, and also for developing a new class of antibiotics; a significant interest of many researchers. Pneumococcal adhesive virulence factor A (PavA) of S. pneumonia is a fibronectin-binding bacterial surface protein (FnBPs), involved in facilitating the colonization of pathogen in host cells. This work presents a dimeric structure of the N-terminal domain of PavA (SpPavA-N) determined to 2.39 Å resolution using X-ray crystallography. Based on the crystal structure, we have identified the difference in the domain II region of SpPavA-N compared to its already known S. suis homolog FBPS-N structure. GBS immunogenic bacterial adhesion protein (BibA) is surface expressed and facilitates evasion of GBS from the human complement system, by sequestering C4b-binding protein (C4BP), a regulator of classical pathway C3-convertase. GBS hosting BibA better escape the complement clearance compared to BibA free GBS. C4BP binding sites were localized in the N-terminal domain of BibA (BibA34-400) previously. We have determined the three-dimensional structure of BibA126-398 fragment at 3.3 Å resolution using X-ray crystallography, which revealed a helical rod-like shape with unique anti-parallel 3-helix bundle motif repeats. Further, using circular dichroism spectrometry and small-angle X-ray scattering techniques, we have proposed a model for the intact BibA34-400 by mimicking the motif repeats on the missing residues. A glutamyl endopeptidase of Staphylococcus epidermidis, extracellular serine protease (Esp) inhibits the S. aureus biofilm formation and growth. Esp was identified to cleave the enzyme autolysin (Atl), shown to be essential for S. aureus biofilm formation. We have determined the crystal structures of seven Esp variants and provide structural insight into the role of N-terminus in the activation of Esp. We have also elucidated the significance of the N-terminal Valine residue and its unique position in the enzyme’s activity, by determining the crystal structure of N-terminus locked Esp variants.

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