Computational analysis identifies druggable mutations in human rBAT mediated Cystinuria.

Area of Science:

• Biochemistry
• Structural Biology
• Pharmacology

Background:

• The mosquito Cqm1 protein binds the Lysinibacillus sphaericus mosquito-larvicidal binary (BinAB) toxin, used for mosquito control.
• The human homolog of Cqm1 is the amino acid transporter protein rBAT (heavy subunit; SLC3A1), which forms a heteromeric system with b0,+AT (light subunit; SLC7A9).
• Mutations in rBAT cause type I Cystinuria, a prevalent disease, making rBAT a potential pharmacological target, yet its 3D structure is unknown.

Purpose of the Study:

• To determine if the BinAB toxin poses a safety risk to humans by assessing its binding to human rBAT.
• To develop homology models for rBAT and the transmembrane b0,+AT subunit.
• To identify potential druggable sites on rBAT for treating type I Cystinuria.

Main Methods:

• Comparative analysis of Cqm1 and human rBAT sequences to assess evolutionary distance and potential toxin binding.
• Homology modeling of the rBAT ectodomain using Cqm1 coordinates and the transmembrane b0,+AT subunit using LAT1 coordinates.
• Mapping and computational simulation-based scoring of pathogenic mutations on the rBAT model.

Main Results:

• A significant evolutionary distance exists between Cqm1 and rBAT, and rBAT lacks the toxin-binding motif, indicating BinAB toxin safety for humans.
• Reliable 3D homology models of rBAT and b0,+AT were constructed.
• Pathogenic mutations on rBAT, not compromising protein fold, cluster on a face likely interacting with b0,+AT, suggesting druggable sites.

Conclusions:

• The BinAB toxin is unlikely to bind to human rBAT, ensuring its safety for human use.
• The developed homology models provide a structural basis for understanding rBAT function and disease mechanisms.
• Specific druggable sites on rBAT have been identified for potential therapeutic interventions in type I Cystinuria.