Structural basis for mammalian nucleotide sugar transport.

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Nucleotide-sugar transporters (NSTs) are essential for cellular glycosylation.
• Dysfunctional NSTs are linked to human diseases and pathogen virulence.

Purpose of the Study:

• To elucidate the structural mechanisms of mammalian NSTs.
• To understand substrate selectivity and transport dynamics of the CMP-sialic acid transporter (CST).

Main Methods:

• X-ray crystallography to determine the structure of mouse CST (mCST) bound to CMP and CMP-sialic acid.
• Analysis of protein-substrate interactions.
• Characterization of substrate-induced conformational changes using tryptophan fluorescence quenching.

Main Results:

• First crystal structures of a mammalian NST (mCST) in complex with its substrates CMP and CMP-sialic acid.
• Detailed visualization of protein-substrate interactions explaining substrate selectivity.
• Identification of a unique lumen-facing partially-occluded conformation and substrate-induced conformational transitions during transport.

Conclusions:

• The structures provide a mechanistic basis for substrate selectivity and transport in NSTs.
• This work offers a framework for understanding disease-associated mutations in NSTs.
• Insights into the transport mechanism of this critical protein family.