Structure-function studies of yeast C-4 sphingolipid long chain base hydroxylase

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Sphingolipids are crucial components of eukaryotic cell membranes.
• The Saccharomyces cerevisiae sphingolipid C-4 long chain base hydroxylase (Sur2p) plays a key role in sphingolipid metabolism.
• Understanding the enzymatic mechanism and active site of Sur2p is vital for elucidating its function.

Purpose of the Study:

• To investigate the roles of putative active site residues in Saccharomyces cerevisiae Sur2p.
• To determine the essentiality of conserved histidine residues within histidine-rich motifs.
• To explore the hydroxylase versus desaturase activities of Sur2p.

Main Methods:

• Site-directed mutagenesis was employed to alter specific amino acid residues in Sur2p.
• Mutant proteins were analyzed for hydroxylase activity both in vivo and in vitro.
• Residues were replaced with corresponding residues from yeast Delta7-sterol-C5(6)-desaturase (Erg3p) to assess functional shifts.

Main Results:

• Replacement of conserved histidine residues in histidine-rich motifs with alanine abolished Sur2p activity.
• An additional conserved histidine residue (His 249) was identified as crucial for enzyme function.
• Several other residues near the histidine-rich cluster were found to be important for hydroxylase activity, but their conversion to Erg3p residues did not confer desaturase activity.

Conclusions:

• Sur2p is a membrane-bound hydroxylase essential for sphingolipid metabolism in Saccharomyces cerevisiae.
• The identified histidine residues are critical components of the Sur2p active site.
• Sur2p belongs to the diiron family of enzymes characterized by eight-histidine motifs.