A fatty acid-binding protein of Streptococcus pneumoniae facilitates the acquisition of host polyunsaturated fatty acids

Jessica M Gullett,Maxime G Cuypers,Matthew W Frank,Stephen W White,Charles O Rock

doi:10.1074/jbc.ra119.010659

Jessica M Gullett, Maxime G Cuypers + Show 3 more

Open Access

https://doi.org/10.1074/jbc.ra119.010659

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Abstract

Streptococcus pneumoniae is responsible for the majority of pneumonia, motivating ongoing searches for insights into its physiology that could enable new treatments. S. pneumoniae responds to exogenous fatty acids by suppressing its de novo biosynthetic pathway and exclusively utilizing extracellular fatty acids for membrane phospholipid synthesis. The first step in exogenous fatty acid assimilation is phosphorylation by fatty acid kinase (FakA), whereas bound by a fatty acid-binding protein (FakB). Staphylococcus aureus has two binding proteins, whereas S. pneumoniae expresses three. The functions of these binding proteins were not clear. We determined the SpFakB1- and SpFakB2-binding proteins were bioinformatically related to the two binding proteins of Staphylococcus aureus, and biochemical and X-ray crystallographic analysis showed that SpFakB1 selectively bound saturates, whereas SpFakB2 allows the activation of monounsaturates akin to their S. aureus counterparts. The distinct SpFakB3 enables the utilization of polyunsaturates. The SpFakB3 crystal structure in complex with linoleic acid reveals an expanded fatty acid-binding pocket within the hydrophobic interior of SpFakB3 that explains its ability to accommodate multiple cis double bonds. SpFakB3 also utilizes a different hydrogen bond network than other FakBs to anchor the fatty acid carbonyl and stabilize the protein. S. pneumoniae strain JMG1 (ΔfakB3) was deficient in incorporation of linoleate from human serum verifying the role of FakB3 in this process. Thus, the multiple FakBs of S. pneumoniae permit the utilization of the entire spectrum of mammalian fatty acid structures to construct its membrane.

Highlights

Streptococcus pneumoniae is responsible for the majority of pneumonia, motivating ongoing searches for insights into its physiology that could enable new treatments
The biosynthetic pathway in the absence of exogenous fatty acids (FA) proceeds via the FASII collection of enzymes to long-chain acyl-acyl carrier protein (ACP) [18], which is distributed to PlsY or PlsC to produce phosphatidic acid, the precursor to all membrane glycerophospholipids [19]
In the presence of exogenous FA, transcription of the FASII genes is potently suppressed by binding of the FabT–acyl-ACP repressor complex to promoters within the FASII gene cluster [6, 10]

Summary

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The Lactobacillales, exemplified by Streptococcus pneumoniae, have a different response These organisms strongly suppress the expression of the genes encoding the FASII enzymes in response to exogenous FA. This response is mediated by the FabT transcriptional repressor (6 –9). FabT bound to acyl-ACP tightly binds to promoters within the FASII gene cluster to potently suppress FASII gene expression [10]. These organisms construct their membrane phospholipids almost exclusively using FA obtained from the environment to acylate both positions of the glycerol-phosphate backbone [3, 11]. The multiple FakBs of S. pneumoniae permit the acquisition and utilization of the entire spectrum of mammalian FA structures to facilitate the acquisition of host FA to construct its membrane at the infection site

Results

Discussion

Experimental procedures