HlgB

HlgB, short for gamma-hemolysin component B, is a secreted protein produced by Staphylococcus aureus as part of the gamma-hemolysin leukotoxin family. It serves as the B subunit of a bicomponent toxin system and typically pairs with HlgA to form HlgAB or with HlgC to form HlgCB. The genes encoding these subunits are organized in the hlgABC operon, and HlgB is typically around 30–35 kDa in size.

The gamma-hemolysin toxins are pore-forming cytotoxins. After secretion, HlgB associates with its partner subunit on the surface of a target cell, the subunits oligomerize, and the complex inserts into the cell membrane to create a pore. This pore formation disrupts cellular ion homeostasis, leading to cell lysis. Leukocytes, especially neutrophils and other immune cells, are among the sensitive targets, contributing to the immune-evasive strategies of S. aureus.

Expression of HlgB and its associated toxins is regulated by bacterial virulence networks, including the agr quorum-sensing system, and can vary across Staphylococcus aureus strains and infection contexts. HlgB is commonly found in many clinical isolates and is co-expressed with HlgA or HlgC, enabling multiple toxin combinations.

Clinically, gamma-hemolysins, including HlgB-containing toxins, are linked to virulence in a range of S. aureus infections. They are studied for their roles in tissue damage and immune cell evasion, and ongoing research examines their contribution to disease severity and their potential as targets for therapeutics or vaccines against staphylococcal infections.