Researchers found that a protein called SufA, made by the common skin bacterium Finegoldia magna, can break down the human antimicrobial peptide LL‑37, which helps fight infections. This means that when this bacterium is present in large numbers, it might weaken one of our natural defenses.

Finegoldia magna is an anaerobic Gram-positive bacterium and commensal, which is also associated with clinically important conditions such as skin and soft tissue infections. This study describes a novel subtilisin-like extracellular serine proteinase of F. magna, denoted SufA (subtilase of Finegoldia magna), which is believed to be the first subtilase described among Gram-positive anaerobic cocci. SufA is associated with the bacterial cell surface, but is also released in substantial amounts during bacterial growth. Papain was used to release SufA from the surface of F. magna and the enzyme was purified by ion-exchange chromatography and gel filtration. A protein band on SDS-PAGE corresponding to the dominating proteolytic activity on gelatin zymography was analysed by MS/MS. Based on the peptide sequences obtained, the sufA gene was sequenced. The gene comprises 3466 bp corresponding to a preprotein of 127 kDa. Like other members of the subtilase family, SufA contains the catalytic triad of aspartic acid, histidine and serine with surrounding conserved residues. A SufA homologue was identified in 33 of 34 investigated isolates of F. magna, as revealed by PCR and immunoprinting. The enzyme forms dimers, which are more proteolytically active than the monomeric protein. SufA was found to efficiently cleave and inactivate the antibacterial peptide LL-37 and the CXC chemokine MIG/CXCL9, indicating that the enzyme promotes F. magna survival and colonization.