Structure of the Fusobacterium nucleatum Sialic Acid Transporter SiaQM Reveals Molecular Determinants of Neu5Ac Binding

核心概念

The structure of the Fusobacterium nucleatum sialic acid transporter SiaQM, both in its unliganded and Neu5Ac-bound forms, reveals the molecular interactions that enable the transport of this important sugar across the bacterial cell membrane.

摘要

The content describes the structural determination and analysis of the Fusobacterium nucleatum sialic acid transporter SiaQM, a key component of the tripartite ATP-independent periplasmic (TRAP) transport system. The key highlights are:

The structures of unliganded and Neu5Ac-bound forms of FnSiaQM were determined using cryo-electron microscopy, both in the inward-facing conformation.
The Neu5Ac-bound structure reveals the binding site and key interactions, including two conserved Na+ binding sites and a third metal-binding site.
Functional studies showed that the interaction between Ser300 in the elevator domain and the C1-carboxylate of Neu5Ac is critical for transport, while Ser345 is dispensable.
The binding pocket is well-suited for drug design, as it has a large cavity and conserved residues interacting with Neu5Ac.
The structures provide fundamental insights into the mechanism of sialic acid transport by TRAP transporters, which are potential targets for combating bacterial infections.

統計資料

Sialic acid (Neu5Ac) concentration in human serum is 1.6–2.2 mM.
The dissociation constant (Kd) of Neu5Ac binding to the periplasmic binding protein FnSiaP is 45 nM.

引述

"Neu5Ac primarily interacts with residues in the elevator domain of the protein, thereby supporting the elevator with an operator mechanism."
"The residues interacting with Neu5Ac are conserved, providing fundamental information required to design inhibitors against this class of proteins."

從以下內容提煉的關鍵洞見

Molecular determinants of Neu5Ac binding to a tripartite ATP independent periplasmic (TRAP) transporter

by Goyal,P., Dh... 於 www.biorxiv.org 03-30-2024

https://www.biorxiv.org/content/10.1101/2024.03.29.587382v1

深入探究

How do the conformational changes in the SiaQM transporter, such as the movement of the elevator domain, facilitate the transport of Neu5Ac from the periplasm to the cytoplasm?

The conformational changes in the SiaQM transporter, particularly the movement of the elevator domain, play a crucial role in facilitating the transport of Neu5Ac from the periplasm to the cytoplasm. The elevator domain acts as a key component in the transport mechanism by undergoing structural rearrangements that allow the substrate to be translocated across the membrane.
When Neu5Ac binds to the transporter, it interacts with specific residues in the elevator domain, triggering a series of conformational changes. The elevator domain acts as a platform that moves the substrate from the periplasmic side to the cytoplasmic side of the membrane. This movement is essential for the successful transport of Neu5Ac into the bacterial cell.
The elevator mechanism in the SiaQM transporter is analogous to other transporters that utilize similar conformational changes to facilitate substrate translocation. By undergoing these structural rearrangements, the transporter can effectively capture, bind, and release Neu5Ac, ensuring its efficient transport across the membrane.

What is the role of the third metal-binding site observed in the FnSiaQM structure, and how does it contribute to the transport mechanism?

The third metal-binding site observed in the FnSiaQM structure plays a significant role in the transport mechanism of the transporter. While the exact nature of this site is still being elucidated, it is distinct from the two known sodium ion binding sites present in the protein. The interactions at this metal-binding site, which is located away from the other binding sites, suggest a unique function in the transport process.
The third metal-binding site likely contributes to the coordination and movement of metal ions within the transporter, which are essential for driving conformational changes required for substrate transport. The presence of this additional metal-binding site indicates a more complex interplay of ions and residues in the transport mechanism of FnSiaQM.
Further studies and mutagenesis experiments are needed to fully understand the role of the third metal-binding site in the transport process and how it coordinates with other elements of the transporter to facilitate the efficient uptake of Neu5Ac by the bacterial cell.

Could the insights from the sialic acid transport system in Fusobacterium nucleatum be applied to develop inhibitors targeting similar transporters in other pathogenic bacteria?

The insights gained from studying the sialic acid transport system in Fusobacterium nucleatum, particularly the structure and function of the SiaQM transporter, hold significant potential for the development of inhibitors targeting similar transporters in other pathogenic bacteria. Understanding the molecular determinants of Neu5Ac binding, the conformational changes in the transporter, and the role of specific residues in substrate transport provides valuable information for designing targeted inhibitors.
By leveraging the conserved structural features and functional mechanisms of TRAP transporters across bacterial species, researchers can develop inhibitors that disrupt the transport of sialic acid and potentially inhibit the growth and virulence of pathogenic bacteria. Targeting key residues involved in substrate binding and transport, as well as the metal-binding sites, could lead to the design of specific inhibitors that interfere with the function of similar transporters in other bacterial pathogens.
Overall, the knowledge gained from studying the sialic acid transport system in Fusobacterium nucleatum can serve as a foundation for the development of novel therapeutic strategies aimed at combating bacterial infections by targeting essential transport mechanisms in pathogenic bacteria.