Hydrolase secretion is a consequence of membrane recycling

Area of Science:

• Cell Biology
• Biochemistry
• Microbiology

Background:

• Acanthamoeba continuously releases lysosomal hydrolases into its environment.
• This secretion is specific to hydrolases and distinct from other cellular proteins.
• The process is energy-dependent and exhibits heterogeneous kinetics.

Purpose of the Study:

• To elucidate the mechanism of lysosomal hydrolase secretion in Acanthamoeba.
• To investigate the role of intracellular compartments and pH in hydrolase release.
• To differentiate the secretion pathway from lysosomal fusion with the plasma membrane.

Main Methods:

• Analysis of secreted proteins and their kinetics.
• Intracellular localization studies of lysosomal hydrolases.
• Investigation of the relationship between pH, membrane binding, and secretion.

Main Results:

• Secreted hydrolases fall into two kinetic groups (approx. 15% and 5% per hour).
• Hydrolases are primarily in secondary lysosomes with differential pH-dependent membrane binding.
• Secretion does not involve direct fusion of secondary lysosomes with the plasma membrane.

Conclusions:

• Acanthamoeba utilizes shuttle vesicles for hydrolase secretion, originating from secondary lysosomes.
• Vesicle fusion with the plasma membrane involves a significant pH shift.
• Heterogeneous secretion kinetics are explained by pH shifts and differential hydrolase-membrane binding.