Abstract
Plasma membrane intrinsic protein is classified into two subfamilies, PIP1 and PIP2. The activities when co-expressing PIP1 and PIP2 were higher than sum of those when PIP1 and PIP2 expressing separately. It's thought that protein traffic and heterotetramer formation participate in this activation mechanism. It is pointed out that this phenomenon might be involved in a possible mechanism for water flow control by aquaporin. Using PIP1 and PIP2 mutants which are inactivated by single amino acid replacement in the pore region, co-expression of normal PIP with PIP mutant was investigated. The results showed that PIP1 was activated by co-expression with the inactivated PIP2 mutant, and also PIP2 was activated with the inactivated PIP1 mutant, as well. Protein-protein interaction experiments by protein complementation method showed that PIP2 monomers assembled to form homo tetramers, but no evidence was obtained for association of PIP1 monomers. Examining the status of PIP1 monomers in plasma membrane or endoplasmic reticulum is progressing now.
