Identification of a Crucial Residue Required for Staphylococcus aureus LukAB Cytotoxicity and Receptor Recognition

Abstract

The bicomponent leukotoxins produced by Staphylococcus aureus kill host immune cells through osmotic lysis by forming ␤-barrel pores in the host plasma membrane. The current model for bicomponent pore formation proposes that octameric pores, comprised of two separate secreted polypeptides (S and F subunits), are assembled from water-soluble monomers in the extracellular milieu and multimerize on target cell membranes. However, it has yet to be determined if all staphylococcal bicomponent leukotoxin family members exhibit these properties. In this study, we report that leukocidin A/B (LukAB), the most divergent member of the leukotoxin family, exists as a heterodimer in solution rather than two separate monomeric subunits. Notably, this property was found to be associated with enhanced toxin activity. LukAB also differs from the other bicomponent leukotoxins in that the S subunit (LukA) contains 33-and 10-amino-acid extensions at the N and C termini, respectively. Truncation mutagenesis revealed that deletion of the N terminus resulted in a modest increase in LukAB cytotoxicity, whereas the deletion of the C terminus rendered the toxin inactive. Within the C terminus of LukA, we identified a glutamic acid at position 323 that is critical for LukAB cytotoxicity. Furthermore, we discovered that this residue is conserved and required for the interaction between LukAB and its cellular target CD11b. Altogether, these findings provide an in-depth analysis of how LukAB targets neutrophils and identify novel targets suitable for the rational design of anti-LukAB inhibitors.

The Bicomponent Pore-Forming Leucocidins of Staphylococcus aureus

“…The formation of stable heterodimers contrasts with that of the other leucocidins, which are believed to exist primarily as water-soluble monomers in solution. It has been proposed that such heterodimers may enhance the potency of LukAB/HG by eliminating the need for a cell surface dimerization step during pore formation (193). Together, these early findings strongly suggest that there are a number of major structural and functional differences between LukAB/HG and the other bicomponent leucocidins.…”

“…Second, a critical amino acid required for LukAB/HG receptor recognition was recently identified within a 10-amino-acid C-terminal extension that is not found in any of the other leucocidins. When the glutamic acid at position 323 of LukAB/HG is mutated to an alanine, the toxin is no longer able to recognize its cellular receptor (CD11b) (discussed below), rendering it inactive on host cells (193). Finally, evidence was recently provided to suggest that LukAB/HG exists as a stable heterodimer in solution.…”

“…3), including N-and C-terminal extensions not present in any of the other toxins (97). Interestingly, this unique C-terminal extension was recently shown to contain a single amino acid that is absolutely critical for the recognition of the host cell surface by LukAB/HG and therefore its lytic activity (193). Such findings further support the notion that ascribing functional activities to LukAB/HG from prior research on and/or structures of the other leucocidins will be challenging.…”

Розвиток Імунної Відповіді При Стафілококовій Пневмонії (Частина 2)

“…Теоретична медицина / Theoretical Medicine Лейкоцидин LukAB является доминирующим токсином, который вызывает гибель человеческих фагоцитов во время стафилококковой инфекции [22]. Jason H. Melehani и соавт.…”

Pertussis vaccines

“…Another major pathogen, Staphylococcus aureus, shares this phenomenon of antigenic conservation and immune evasion of phagocytosis. B. pertussis ACT and S. aureus LukAB both bind to the neutrophil receptor C11b [22], which is in contrast to other pathogens such as the pneumococcus and meningococcus that appear to rely upon antigenic variability to avoid the host immune system.…”