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

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 SpFakB1and 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 (⌬fakB3) 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.

Induction of Daptomycin Tolerance in Enterococcus faecalis by Fatty Acid Combinations

“…To determine whether the presence of the protective fatty acids found in serum, namely, oleic and linoleic acids, could ameliorate the negative growth impacts of palmitic and stearic acids, we simulated the fatty acid membrane profile upon serum supplementation by adding each of these fatty acids to the culture (referred to as SLOP, i.e., stearic acid, linoleic acid, oleic acid, and palmitic acid). Note that as the concentration of each specific fatty acid varies in serum given the individual and the testing method, we opted to use 5 μg ml −1 as this concentration is below what has been measured or used in other in vitro studies ( 13 – 16 ).…”

“…In S. aureus and Streptococcus pneumoniae , exogenous fatty acids that associate with the membrane are bound by a specific FakB binding protein that, in concert with FakA, phosphorylates the fatty acid, activating it for use in lipid biosynthesis ( 33 ). Biochemical analyses suggest that there is a specific FakB binding protein for saturated fatty acids, another one for unsaturated fatty acids, and, in the case of S. pneumoniae , a third for polyunsaturated fatty acids ( 13 , 34 ). As oleic acid addition seems to prevent utilization of stearic acid by OG1RF, this may suggest that the specificity of the FakB proteins in E. faecalis does not follow that of S. aureus or S. pneumoniae .…”

Cadmium stress dictates central carbon flux and alters membrane composition in Streptococcus pneumoniae

“…Membrane composition and fluidity is altered by Cd 2+ stress. In addition to de novo FA biosynthesis by the FASII system, the pneumococcus can incorporate exogenous FAs into its membrane via FA phosphorylation using the FakAB1B2B3 and PlsXY systems 61,63,64 . This facilitates phospholipid acquisition without use of the energy intensive FASII system.…”

The Bactericidal Fatty Acid Mimetic 2CCA-1 Selectively Targets Pneumococcal Extracellular Polyunsaturated Fatty Acid Metabolism

“…FabT has increased affinity for DNA binding in the presence of a corepressor, such as the FASII operon-encoded acyl carrier protein 1 (ACP1; locus tag SPD_0381) that mediates feedback inhibition of the FASII system when acylated with long acyl chains ( 15 ). Also, recently the auxiliary acyl carrier protein 2 (ACP2; locus tag SPD_0044) was described to mediate FabT binding as a cofactor when acylated with extracellular fatty acids ( 16 – 18 ). Biochemical regulation of de novo fatty acid synthesis occurs at its first step through acetyl-CoA carboxylase (ACC) inhibition by an unknown ligand that is postulated to be either acyl-ACP or acyl-PO 4 (11).…”

“…Biochemical regulation of de novo fatty acid synthesis occurs at its first step through acetyl-CoA carboxylase (ACC) inhibition by an unknown ligand that is postulated to be either acyl-ACP or acyl-PO 4 (11). In Gram-positive bacteria, such as pneumococci, extracellular fatty acids are activated by a fatty acid kinase (FakA) and by fatty acid binding proteins (FakB) to initiate phospholipid synthesis ( 16 , 19 , 20 ). Phosphorylated fatty acids (acyl-PO 4 ) serve as substrates for PlsY for lysophosphatidic acid formation from glycerol-3-phosphate (G3P) or, after conversion by the acyl:PO 4 transacylase PlsX to acyl-ACP, can be used as the substrate for PlsC to acylate G3P in position 2 for phosphatidic acid biosynthesis ( 21 – 23 ).…”