Crystal structure of a eukaryotic phosphate transporter

Area of Science:

• Structural biology
• Biochemistry
• Molecular biology

Background:

• Phosphate is vital for cellular functions, including energy storage and synthesis.
• Proton-coupled transporters, like the major facilitator superfamily (MFS), are key for phosphate uptake and sensing in organisms.
• Understanding these transporters is crucial for various biological processes and disease research.

Purpose of the Study:

• To determine the high-resolution structure of a fungal high-affinity phosphate transporter, PiPT.
• To elucidate the transport mechanism and substrate binding site of PiPT.
• To provide structural insights into related human transporter families (SLC22).

Main Methods:

• X-ray crystallography was used to determine the 2.9 Å structure of PiPT.
• The structure was analyzed to identify proton and phosphate pathways and binding sites.
• Homology modeling was employed to study related human SLC22 transporters.

Main Results:

• The structure of PiPT was resolved in an inward-facing occluded state, revealing bound phosphate.
• Evidence for distinct proton and phosphate exit pathways was observed.
• A modified asymmetrical 'rocker-switch' mechanism is proposed for PiPT transport.
• Structural models of SLC22 transporters suggest substrate binding and charge selectivity principles.

Conclusions:

• The PiPT structure provides a detailed molecular understanding of high-affinity phosphate transport.
• The findings illuminate the transport mechanism of MFS transporters and phosphate uptake.
• This research offers a structural basis for understanding human SLC22 transporters, relevant to cancer drug resistance.