Annual Meeting

Arginine tango

How a bacterial enzyme enables immune evasion
Nicole Lynn
April 27, 2021
The bacteria Staphylococcus aureus, found on human skin and in the nose, is the leading pathogen among dermal and soft tissue infections. In the immunocompromised or those in hospital settings, S. aureus can cause serious infections.

As a means to evade the host immune response, S. aureus uses an enzyme called oleate hydratase, or OhyA, to inactivate antimicrobial unsaturated fatty acids in the membrane that would otherwise inhibit bacterial growth. Research scientists at St. Jude Children’s Research Hospital reported today the structure and catalytic mechanism of OhyA.

Christopher Radka of St. Jude’s Department of Infectious Diseases describes the research during a presentation Tuesday at 2 p.m. EDT at the 2021 ASBMB Annual Meeting, held in conjunction with the Experimental Biology conference.

Radka and colleagues used X-ray crystallography to determine the structure of OhyA. Solving and evaluating multiple OhyA crystal structures highlighted a coordinated dance that occurs between key arginine residues and the unsaturated fatty acid substrate in the active site of the enzyme, a process facilitated by the nucleotide cofactor FAD.
Radka et al. JBC 2021
The 18:1 fatty acid substrate (black) first encounters Arg81 of OhyA, which blocks the entrance to the active site until FAD binds. Upon FAD (cyan) binding, Arg81 rotates, allowing the substrate into the active site. Arg81 continually rotates the substrate in the active site, allowing for inactivation of the antimicrobial fatty acid substrate to hydroxy fatty acid, or h18:0. After catalysis, Arg78 lunges to expel h18:0 from the active site.

In this dance, the substrate is first guided into the binding tunnel by the oleate carbonyl of OhyA, then encounters its first arginine dance partner (Arg81) at the entrance of the active site. FAD binding then triggers the rotation of Arg81 that guides the fatty acid as it curls into the active site. After catalysis, a second arginine (Arg78) rotates behind the fatty acid carboxyl to release the hydroxylated product from the active site.
“What’s novel about the (active site) is how these conserved arginines guide the substrate through the donut-shaped active site,” Radka said. “Here, the arginines dance like two partners in a tango.”

This highly choreographed dance controls how the fatty acid substrate moves into and out of the active site. “In this coordinated tango at the active site, the FAD is the dramatic third character whose role is to come in and advance the dance so the chemistry can occur,” Radka said.

In this reaction, FAD remains oxidized and unconsumed. This quality is advantageous for industrial biotechnology research looking to use OhyA; FAD-dependent reactions often consume FADH2 and require continued starting product, which can be costly.

Future goals for this research include determining the structural elements required for S. aureus OhyA to remove antimicrobial fatty acids from the membrane.
Nicole Lynn

Nicole Lynn is a Ph.D. candidate at UCLA and a volunteer writer for ASBMB Today.

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