Acyl-chain selectivity and physiological roles of Staphylococcus aureus fatty acid–binding proteins

Abstract

Edited by George M. Carman Fatty acid (FA) kinase produces acyl-phosphate for the synthesis of membrane phospholipids in Gram-positive bacterial pathogens. FA kinase consists of a kinase protein (FakA) that phosphorylates an FA substrate bound to a second module, an FA-binding protein (FakB). Staphylococcus aureus expresses two distinct, but related, FakBs with different FA selectivities. Here, we report the structures of FakB1 bound to four saturated FAs at 1.6-1.93 Å resolution. We observed that the different FA structures are accommodated within a slightly curved hydrophobic cavity whose length is governed by the conformation of an isoleucine side chain at the end of the tunnel. The hydrophobic tunnel in FakB1 prevents the binding of cis-unsaturated FAs, which are instead accommodated by the kinked tunnel within the FakB2 protein. The differences in the FakB interiors are not propagated to the proteins' surfaces, preserving the proteinprotein interactions with their three common partners, FakA, PlsX, and PlsY. Using cellular thermal shift analyses, we found that FakB1 binds FA in vivo, whereas a significant proportion of FakB2 does not. Incorporation of exogenous FA into phospholipid in ⌬fakB1 and ⌬fakB2 S. aureus knockout strains revealed that FakB1 does not efficiently activate unsaturated FAs. FakB2 preferred unsaturated FAs, but also allowed the incorporation of saturated FAs. These results are consistent with a model in which FakB1 primarily functions in the recycling of the saturated FAs produced by S. aureus metabolism, whereas FakB2 activates host-derived oleate, which S. aureus does not produce but is abundant at infection sites.

Lipidomic and Ultrastructural Characterization of Cell Envelope ofStaphylococcus aureusGrown in the Presence of Human Serum

“…1). The two-component fatty acid kinase system (FakA/B) produces fatty acyl-phosphate via FakA that phosphorylates fatty acids bound to FakB1 or FakB2 binding proteins, which have preferential specificities for SCFAs and SCUFAs, respectively (21). The resulting fatty acyl-phosphate is then incorporated into phospholipids via PlsXY.…”

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

“…The Bacillales, exemplified by Staphylococcus aureus, do not genetically suppress the genes of type II FA biosynthesis (FASII) in the presence of exogenous FA (3). Rather, FASII continues to produce primarily anteiso15:0 that is placed in the 2-position, and the exogenous long-chain saturated and monounsaturated FA are activated by FA kinase and placed into the 1-position (4,5). The Lactobacillales, exemplified by Streptococcus pneumoniae, have a different response.…”

“…The ability of FA kinase to activate FA encountered in the environment is conferred by the FA selectivities of the FakB component. S. aureus expresses two FakBs (1,5). SaFakB1 is specific for saturated FA (16:0), whereas SaFakB2 selectively binds monounsaturated FA (18:1) (1,5,12).…”

“…S. aureus expresses two FakBs (1,5). SaFakB1 is specific for saturated FA (16:0), whereas SaFakB2 selectively binds monounsaturated FA (18:1) (1,5,12). S. aureus does not synthesize unsaturated FA, so SaFakB1 is the housekeeping protein and SaFakB2 is responsible for the uptake of host monounsaturated FA (1,5,12).…”

“…SaFakB1 is specific for saturated FA (16:0), whereas SaFakB2 selectively binds monounsaturated FA (18:1) (1,5,12). S. aureus does not synthesize unsaturated FA, so SaFakB1 is the housekeeping protein and SaFakB2 is responsible for the uptake of host monounsaturated FA (1,5,12). S. pneumoniae encodes three FakB-binding proteins suggesting an expanded repertoire of FA-binding capabilities to enable the acquisition of environmental FA to replace de novo biosynthesis.…”