Golgi localization and functional expression of human uridine diphosphatase

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Ecto-ATPases (E-ATPases) are enzymes involved in extracellular ATP metabolism.
• The localization and function of many E-ATPase family members, particularly within intracellular organelles, remain poorly understood.
• Nucleoside hydrolysis plays a critical role in cellular signaling and metabolism.

Purpose of the Study:

• To identify and characterize a novel mammalian E-ATPase family member.
• To determine the subcellular localization and substrate specificity of the identified enzyme.
• To elucidate the orientation of the enzyme's active site within the cell.

Main Methods:

• Cloning of a full-length cDNA encoding a human E-ATPase from a brain cDNA library.
• Heterologous expression of the cloned cDNA in COS-7 cells.
• Biochemical assays to measure nucleoside phosphatase activity with various substrates and divalent cations.
• Immunofluorescence staining to determine protein localization.
• Functional assays using Triton X-100 and alamethicin to probe active site accessibility.

Main Results:

• A 610-amino acid protein with two putative transmembrane domains was identified.
• Heterologous expression led to increased intracellular membrane-bound nucleoside phosphatase activity, highest with UDP.
• Enzyme activity was significantly stimulated by Ca2+, Mg2+, and Mn2+.
• Immunofluorescence localized the protein to the Golgi apparatus.
• Increased UDP hydrolysis with Triton X-100 and alamethicin suggests a luminal active site.

Conclusions:

• This study reports the first identification of a mammalian Golgi luminal UDPase gene.
• The characterized enzyme plays a role in UDP hydrolysis within the Golgi lumen.
• The findings provide insights into the diversity and localization of E-ATPase superfamily members in mammals.