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Characterization of Rabaptin-5 γ Isoform

E. V. Korobko1, S. L. Kiselev1,2, and I. V. Korobko1*

1Institute of Gene Biology, Russian Academy of Sciences, ul. Vavilova 34/5, 119334 Moscow, Russia; fax: (499) 135-4105; E-mail: igorvk@igb.ac.ru; korobko1305@gmail.com

2Present address: Vavilov Institute of General Genetics, ul. Gubkina 3, 119911 Moscow, Russia

* To whom correspondence should be addressed.

Received March 3, 2014; Revision received May 29, 2014
Rab GTPases are key regulators of intracellular membrane traffic acting through their effector molecules. Rabaptin-5 is a Rab5 effector in early endosome fusion and connects Rab5- and Rab4-positive membrane compartments owing to its ability to interact with Rab4 GTPase. Recent studies showed that Rabaptin-5 transcript is subjected to extensive alternative splicing, thus resulting in expression of Rabaptin-5 isoforms mostly bearing short deletions in the polypeptide chain. As interactions of a Rab GTPase with different effectors lead to different responses, functional characterization of Rabaptin-5 isoforms becomes an attractive issue. Indeed, it was shown that Rab GTPase effector properties of Rabaptin-5 and its α and δ isoforms are different. This work focused on another Rabaptin-5 isoform, Rabaptin-5γ. Despite its ability to interact with Rab5, endogenously produced Rabaptin-5γ was absent from early endosomes. Rather, it was found to be tightly associated with trans-Golgi network and partially localized to a Rab4-positive membrane compartment. The revealed intracellular localization of Rabaptin-5γ indicates that it is not involved in Rab5-driven events; rather, it functions in other membrane transport steps. Our study signifies the role of alternative splicing in determination of functional activities of Rab effector molecules.
KEY WORDS: intracellular membrane transport, early endosomes, trans-Golgi network, Rab5 small GTPase, Rab4 small GTPase, small GTPase effectors, Rabaptin-5γ

DOI: 10.1134/S000629791409003X