The Thermotoga maritima Trk potassium transporter--from frameshift to function

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• The TrkA component of the Thermotoga maritima Trk potassium transporter was initially believed to be non-functional due to a frameshift mutation.
• Expression studies revealed a functional two-protein complex, TM1088A/B, involved in potassium transport.

Purpose of the Study:

• To investigate the function and structure of the Thermotoga maritima TrkA protein.
• To determine the role of TM1088A/B in potassium transport and its interaction with other proteins.

Main Methods:

• Genetic complementation of potassium transport-deficient Escherichia coli mutants.
• Protein structure analysis using X-ray crystallography.
• Ligand binding assays to study nucleotide interactions with TM1088A.

Main Results:

• TM1088A/B forms a functional complex with the membrane protein TM1089, essential for potassium transport.
• TM1088A possesses a Rossmann fold, indicative of an NAD+ binding site, and structural similarities to potassium channel proteins.
• ATP, ADP, and AMP stabilize TM1088A, with AMP identified as a natural ligand at the nucleotide binding site. Mutations in this site did not abolish in vitro function.

Conclusions:

• A novel two-subunit TrkA protein class is identified, potentially widespread across organisms.
• A subclass of these TrkA proteins may function independently of a membrane-spanning subunit, as seen in Mycobacterium tuberculosis, possibly requiring a unique partner protein or serving an alternative role.