Identification of a novel host-specific IgG protease in Streptococcus phocae subsp. phocae

Area of Science:

• Microbiology
• Immunology
• Marine Mammal Health

Background:

• Streptococcus phocae subsp. phocae is an opportunistic pathogen causing severe infections in marine mammals.
• This bacterium plays a significant role in harbor seal infections, especially when co-infected with phocine distemper virus.
• Previous observations indicated bacterial supernatant degrading immunoglobulin G (IgG) in harbor seal serum.

Purpose of the Study:

• To identify and characterize the secreted IgG-cleaving protease from Streptococcus phocae subsp. phocae.
• To understand the role of this protease in the bacterium's pathogenicity and host interaction.

Main Methods:

• Protease inhibitor profiling using iodoacetamide and Z-LVG-CHN2 to determine enzyme class.
• Cross-reactivity testing with antibodies against Streptococcus pyogenes IdeS.
• Identification of the gene encoding the protease via inverse PCR.
• Recombinant expression and characterization of the purified enzyme (IdeP).

Main Results:

• Protease activity was inhibited by reagents targeting cysteine proteases.
• An antibody against S. pyogenes IdeS showed cross-reactivity, suggesting a similar enzyme.
• The IgG-cleaving enzyme was identified as IdeP (Immunoglobulin G degrading enzyme of S. phocae subsp. phocae).
• Recombinant IdeP specifically cleaved IgG from grey and harbor seals, but not from porpoises or non-marine mammals.

Conclusions:

• IdeP is a novel cysteine protease from S. phocae subsp. phocae that degrades marine mammal IgG.
• This enzyme is crucial for immune evasion and represents a host-specific adaptation of the pathogen.
• The findings provide insights into the pathogenesis of S. phocae subsp. phocae in marine mammals, particularly seals.