Iron homeostasis in the mammalian host limits the availability of iron to invading pathogens and is thought to restrict iron availability for microbes inhabiting mucosal surfaces. The presence of surface receptors for the host iron-binding glycoproteins transferrin (Tf) and lactoferrin (Lf) in globally important Gram-negative bacterial pathogens of humans and food production animals suggests that Tf and Lf are important sources of iron in the upper respiratory or genitourinary tracts, where they exclusively reside. Lf receptors have the additional function of protecting against host cationic antimicrobial peptides, suggesting that the bacteria expressing these receptors reside in a niche where exposure is likely. In this review we compare Tf and Lf receptors with respect to their structural and functional features, their role in colonization and infection, and their distribution among pathogenic and commensal bacteria.
Bacteria that inhabit the mucosal surfaces of the respiratory and genitourinary tracts of mammals encounter an iron-deficient environment because of iron sequestration by the host iron-binding proteins transferrin and lactoferrin. Lactoferrin is also present in high concentrations at sites of inflammation where the cationic, antimicrobial peptide lactoferricin is produced by proteolysis of lactoferrin. Several Gram-negative pathogens express a lactoferrin receptor that enables the bacteria to use lactoferrin as an iron source. The receptor is composed of an integral membrane protein, lactoferrin binding protein A (LbpA), and a membrane-bound lipoprotein, lactoferrin binding protein B (LbpB). LbpA is essential for growth with lactoferrin as the sole iron source, whereas the role of LbpB in iron acquisition is not yet known. In this study, we demonstrate that LbpB from 2 different species is capable of providing protection against the killing activity of a human lactoferrin-derived peptide. We investigated the prevalence of lactoferrin receptors in bacteria and examined their sequence diversity. We propose that the protection against the cationic antimicrobial human lactoferrin-derived peptide is associated with clusters of negatively charged amino acids in the C-terminal lobe of LbpB that is a common feature of this protein.
Background: Student mentoring is an important aspect of undergraduate medical education. While medical schools often assign faculty advisors to medical students as mentors to support their educational experience, it is possible for the students to pursue mentors informally. The possible role of these informal mentors and their interactions with the students in a faculty mentorship program has not been reported. This study builds upon previous work that suggested many students have informal mentors, and that there might be interplay between these two types of mentors. This study was conducted to report the experience of undergraduate medical students in a faculty mentorship program of their faculty mentors and if applicable, of their informal mentors. Methods: One month before residency (post-graduate training for Canadians) ranking, the survey was administered to the graduating class of 2014 at the University of Calgary's Cumming School of Medicine. The survey was created from focus groups of the previous graduating class of 2013. The survey investigated meeting characteristics and the students' perceptions of faculty advisors and informal mentors, and the students' intended choice for residency. Results: The study response rate was 86 % (95 of 111); 58 % (54 of 93) of the students reported having an informal mentor. There was no reported difference in satisfaction ratings of the Faculty mentorship program between students with only faculty mentors and those with also informal mentors. Students' reporting of their satisfaction with the Facultymentorship program and the faculty mentors did not differ between the students with informal mentors and those with faculty mentors only. The students' meeting frequency, discussed topics, and perceived characteristics of faculty mentors were not associated with having an informal mentor. The students generally perceived their informal mentors more positively than their faculty mentors. The reported student career intention was associated with the discipline of informal mentors and not with the discipline of faculty mentors. Conclusions: Informal mentorship was common for medical students. The presence of an informal mentor was not associated with dissatisfaction with the Faculty advisor or with the mentorship program. It is likely students may pursue informal mentorship for career-related reasons.
A variety of Gram-negative pathogens possess host-specific lactoferrin (Lf) receptors that mediate the acquisition of iron from host Lf. The integral membrane protein component of the receptor, lactoferrin binding protein A specifically binds host Lf and is required for acquisition of iron from Lf. In contrast, the role of the bi-lobed surface lipoprotein, lactoferrin binding protein B (LbpB), in Lf binding and iron acquisition is uncertain. A common feature of LbpBs from most species is the presence of clusters of negatively charged amino acids in the protein's C-terminal lobe. Recently it has been shown that the negatively charged regions from the Neisseria meningitidis LbpB are responsible for protecting against an 11 amino acid cationic antimicrobial peptide (CAP), lactoferricin (Lfcin), derived from human Lf. In this study we investigated whether the LbpB confers resistance to other CAPs since N. meningitidis is likely to encounter other CAPs from the host. LbpB provided protection against the cathelicidin derived peptide, cathelicidin related antimicrobial peptide (mCRAMP), but did not confer protection against Tritrp 1 or LL37 under our experimental conditions. When tested against a range of rationally designed synthetic peptides, LbpB was shown to protect against IDR-1002 and IDR-0018 but not against HH-2 or HHC10.
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