<p>Two species of <i>Neisseria</i>, <i>N. meningitidis</i> and <i>N.
gonorrhoeae</i>, are obligate human pathogens that cause meningitis and
gonorrhea, respectively. Although generally asymptomatic, <i>N. meningitidis</i>
can cause invasive meningococcal disease with high mortality rate. Due to
emerging antibiotic resistance strains of <i>N. gonorrhoeae</i>, the Centers
for Disease Control and Prevention (CDC) have designated it as an urgent threat
to public health. Therefore, immediate interventions are required for fight
against these Neisserial pathogens. Iron is an essential nutrient for all
bacteria, including <i>Neisseria</i>. However, free iron is scarce in human,
therefore, <i>Neisseria</i> have evolved to acquire iron from host proteins.
These iron acquisition systems are immunogenic and important for infection and
are promising therapeutic targets.</p>
<p> In the
host, lactoferrin sequesters free iron and limits iron availability to
pathogens. However, <i>Neisseria</i> have evolved machinery to hijack iron directly
from lactoferrin itself. Lactoferrin
binding proteins, LbpA and LbpB, are outer membrane proteins that together
orchestrate the acquisition of iron from lactoferrin. Additionally, LbpB serves
an additional role in providing protection against host cationic antimicrobial
peptides and innate immune response. Despite studies aimed at deciphering the
roles of LbpA and LbpB, the molecular mechanisms underpinning iron acquisition
and immune protection remain unknown. Here, we investigated the role of the lactoferrin
binding proteins in iron acquisition and protection against cationic
antimicrobial peptides. We obtained three-dimensional structures of <i>Neisseria</i>
LbpA and LbpB in complex with lactoferrin using cryo-electron microscopy and
X-ray crystallography. These structures show that both LbpA and LbpB bind to
C-lobe of lactoferrin, albeit at distinct sites. Structural analyses show that
while lactoferrin maintains its iron-bound closed conformation in the
LbpB-lactoferrin complex, it undergoes a large conformational change from an
iron-bound closed to an iron-free open conformation upon binding to LbpA. This
observation suggest that LbpA alone can trigger the extraction of iron from
lactoferrin. Our studies also provide an explanation for LbpB’s preference
towards holo-lactoferrin over apo-lactoferrin and LbpA’s inability to
distinguish between holo- and apo-lactoferrin. Furthermore, using mutagenesis
and binding studies, we show that anionic loops in the C-lobe of LbpB
contribute to binding the cationic antimicrobial peptide lactoferricin.
Solution scattering studies of the LbpB-lactoferricin complex showed that LbpB
undergoes a small conformational change upon peptide binding.</p>
Together,
our studies provide structural insights into the role of the lactoferrin
binding proteins in iron acquisition and evasion of the host immune defenses.
Moreover, this work lays the foundation for structure-based design of
therapeutics against <i>Neisseria</i> targeting the lactoferrin binding
proteins.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/17263904 |
| Date | 17 December 2021 |
| Creators | Ravi Yadav (11850101) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Structural_And_Functional_Studies_Of_Neisserial_Lactoferrin_Binding_Proteins/17263904 |
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