Expression and processing of recombinant human galactosylceramidase

Area of Science:

• Biochemistry
• Cell Biology
• Enzyme Kinetics

Background:

• Human galactosylceramidase (GALC) is crucial for myelin maintenance.
• Defects in GALC cause globoid cell leukodystrophy, a severe lysosomal storage disorder.
• Understanding GALC processing and activity is vital for therapeutic development.

Purpose of the Study:

• To investigate the structure and processing of human GALC in overexpressing Chinese hamster ovary (CHO) cells.
• To determine the cellular uptake and lysosomal processing of the GALC precursor enzyme.
• To elucidate the functional significance of GALC fragments and identify the active enzyme form.

Main Methods:

• Generation of stable CHO cell transformants overexpressing human GALC.
• Characterization of intracellular and secreted GALC forms using SDS-PAGE and Western blotting.
• Analysis of GALC uptake by fibroblasts via the mannose-6-phosphate receptor.
• Investigation of GALC processing in the presence of lysosomotropic agents (chloroquine, NH4Cl).
• Assessment of GALC activity in cells expressing wild-type and mutant forms.

Main Results:

• Intracellular GALC comprised 50- and 30-kDa proteins, while secreted GALC was an 80-kDa precursor.
• The 80-kDa precursor was efficiently taken up by fibroblasts through the mannose-6-phosphate receptor.
• GALC processing into 50- and 30-kDa fragments occurred within lysosomes, inhibited by chloroquine and NH4Cl.
• Globoid cell leukodystrophy-associated GALC mutations impaired this fragmentation.
• Neither the 50- nor 30-kDa fragment exhibited GALC activity when expressed independently.

Conclusions:

• The 80-kDa GALC precursor is processed into smaller fragments within the lysosome.
• Lysosomal degradation is essential for generating mature, active GALC.
• The complete structure of GALC is necessary for its enzymatic activity; fragments are inactive.
• Understanding GALC processing is critical for developing therapies for globoid cell leukodystrophy.