The in vitro permeability of yeast peroxisomal membranes is caused by a 31 kDa integral membrane protein

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Peroxisomal membrane proteins (PMPs) play crucial roles in peroxisome function.
• Integral membrane proteins with pore-forming capabilities are essential for selective transport across membranes.

Purpose of the Study:

• To purify and characterize a major integral peroxisomal membrane protein (PMP31) from Hansenula polymorpha.
• To investigate the functional properties, specifically pore-forming activity, of purified PMP31.

Main Methods:

• Purification of PMP31 from isolated peroxisomal membranes using FPLC after Triton X-100 solubilization.
• Construction of proteoliposomes with purified PMP31 and asolectin.
• Assessment of selective permeability using [14C]sucrose/[3H]dextran leakage ratios.
• Measurement of membrane potential (delta psi) generation in response to potassium diffusion gradients.

Main Results:

• PMP31 was purified to homogeneity and showed cross-reactivity with antibodies against mitochondrial porin.
• Proteoliposomes containing PMP31 exhibited selective permeability, indicated by altered sucrose and dextran leakage.
• The presence of PMP31 negatively affected membrane potential generation in proteoliposomes, both with and without a cytochrome c oxidase system.
• Glutaraldehyde treatment abolished sucrose leakage but did not affect membrane potential measurements, suggesting distinct mechanisms.

Conclusions:

• Hansenula polymorpha PMP31 possesses pore-forming properties, contributing to selective membrane permeability.
• PMP31 influences the electrochemical gradient across the peroxisomal membrane.
• The findings suggest PMP31 may play a role in regulating solute transport and membrane potential within peroxisomes.