Polyprenol phosphate as an acceptor of mannose from guanosine diphosphate mannose in Aspergillus niger

Area of Science:

• Biochemistry
• Mycology
• Cell Biology

Background:

• Fungal cell wall biosynthesis involves complex pathways.
• Lipid intermediates play critical roles in glycosylation processes.
• Aspergillus niger is a model organism for studying fungal metabolism.

Purpose of the Study:

• To investigate the biosynthesis of mannolipids in Aspergillus niger.
• To identify the specific lipid acceptor involved in mannan formation.
• To elucidate the enzymatic machinery responsible for mannose transfer.

Main Methods:

• Radiolabeling of Aspergillus niger with [2-(14)C]mevalonate and (32)P(i).
• Enzymatic assays using GDP-[14C]mannose and particulate enzyme preparations.
• Chromatographic analysis and characterization of lipid products.
• Identification of mannolipid structure and its precursor.

Main Results:

• A novel lipid, identified as exo-methylene-hexahydropolyprenol phosphate, was formed.
• Incubation with GDP-[14C]mannose yielded mannose 1-phosphate, mannose, mannan, and a mannolipid.
• The mannolipid was characterized as exo-methylene-hexahydropolyprenol phosphate mannose.
• Enzyme activity demonstrated a mannose transferase utilizing the identified lipid phosphate.

Conclusions:

• Aspergillus niger possesses a mannose transferase that accepts exo-methylene-hexahydropolyprenols phosphate.
• This mannolipid serves as a key intermediate in the biosynthesis of fungal mannan.
• The findings provide insights into glycosylation pathways analogous to bacterial systems.