Bacterial lipoproteins (Lpps) are a class of membrane-associated proteins universally distributed among all bacteria. A characteristic N-terminal cysteine residue that is variably acylated anchors C-terminal globular domains to the extracellular surface, where they serve numerous roles, including in the capture and transport of essential nutrients. Lpps are also ligands for the Toll-like receptor 2 (TLR2) family, a key component of the innate immune system tasked with bacterial recognition. While Lpp function is conserved in all prokaryotes, structural heterogeneity in the N-terminal acylation state is widespread among Firmicutes and can differ between otherwise closely related species. In this study, we identify a novel two-gene system that directs the synthesis of N-acylated Lpps in the commensal and opportunistic pathogen subset of staphylococci. The two genes, which we have named the lipoprotein N-acylation transferase system (Lns), bear no resemblance to previously characterized N-terminal Lpp tailoring enzymes. LnsA (SAOUHSC_00822) is an NlpC/P60 superfamily enzyme, whereas LnsB (SAOHSC_02761) has remote homology to the CAAX protease and bacteriocin-processing enzyme (CPBP) family. Both LnsA and LnsB are together necessary and alone sufficient for N-acylation in Staphylococcus aureus and convert the Lpp chemotype from diacyl to triacyl when heterologously expressed in Listeria monocytogenes. Acquisition of lnsAB decreases TLR2-mediated detection of S. aureus by nearly 10-fold and shifts the activated TLR2 complex from TLR2/6 to TLR2/1. LnsAB thus has a dual role in attenuating TLR2 signaling in addition to a broader role in bacterial cell envelope physiology. IMPORTANCE Although it has long been known that S. aureus forms triacylated Lpps, a lack of homologs to known N-acylation genes found in Gram-negative bacteria has until now precluded identification of the genes responsible for this Lpp modification. Here, we demonstrate N-terminal Lpp acylation and chemotype conversion to the tri-acylated state is directed by a unique acyl transferase system encoded by two noncontiguous staphylococci genes (lnsAB). Since triacylated Lpps stimulate TLR2 more weakly than their diacylated counterparts, Lpp N-acylation is an important TLR2 immunoevasion factor for determining tolerance or nontolerance in niches such as in the skin microbiota. The discovery of the LnsAB system expands the known diversity of Lpp biosynthesis pathways and acyl transfer biochemistry in bacteria, advances our understanding of Lpp structural heterogeneity, and helps differentiate commensal and noncommensal microbiota.

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1. Seventy-six patients with fracture of the upper end of the femur were examined phlebographically for evidence of thrombosis. The patients were randomly divided into two groups : one was given phenindione post-operatively ; the other acted as a control. 2. Analysis of the select series showed that the incidence of venous thrombosis in the anticoagulation group (19 per cent) was significantly less than that in the control group (48 per cent). 3. However, analysis of the complete series failed to show that the incidence of venous thrombosis in the anticoagulation group was significantly less than in the control group. 4. The number of bleeding complications in the anticoagulation group (47 per cent) exceeded those in the control group (16 per cent). The only life-endangering haemorrhage occurred in a patient who had not received an anticoagulant for five months. 5. We were unable to show that the fracture significantly influenced the site or the incidence of venous thrombosis. 6. No correlation was found between the clinical and phlebographic diagnosis of venous thrombosis. 7. It is concluded that the early use of a prophylactic anticoagulant is an effective means of reducing the incidence of venous thrombosis in patients with a fracture about the hip.

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