Complex sentence: Membrane fusion of the phagosome and lysosome is regulated by the Rab5 protein, a G protein that allows the exchange of material between these two organelles but prevents complete fusion of their membranes.
Split into simpler sentences: Membrane fusion of the phagosome and lysosome is regulated by Rab 5 protein. This G Protein allows the exchange of material between these two organelles but prevents complete fusion of their membranes.