Modulation of monocarboxylate transporter 8 oligomerization by specific pathogenic mutations

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Monocarboxylate transporter 8 (MCT8) facilitates iodothyronine transport, crucial for thyroid hormone regulation.
• Mutations in MCT8 cause severe X-linked psychomotor retardation due to impaired transport function.
• The precise molecular mechanisms linking MCT8 mutations to transport deficiencies remain unclear.

Purpose of the Study:

• To investigate the relationship between pathogenic MCT8 mutants and their dimerization capacity.
• To explore dimerization as a potential regulatory parameter for MCT8 transport function.
• To correlate genotype with molecular features and cellular localization of MCT8 variants.

Main Methods:

• In vitro analysis of fourteen pathogenic MCT8 variants for oligomerization capacity.
• Assessment of MCT8 dimer formation and distribution in a cellular context.
• Integration of functional data with structural-mechanistical insights.

Main Results:

• Mutations near the substrate channel (S194F, A224T, L434W, R445C) inhibited MCT8 dimerization.
• Substitutions in transmembrane helix 2 (del230F, V235M, ins236V) enhanced MCT8 dimerization.
• Distinct patterns of MCT8 dimer formation and cellular localization were observed for different mutants.

Conclusions:

• MCT8 dimerization is a critical factor influencing its transport function.
• Specific mutations disrupt or promote MCT8 oligomerization, affecting protein organization.
• Findings provide novel insights into MCT8 structure-function relationships and may apply to other MFS members.