Assays and properties of the ArfGAPs, AMAP1 and AMAP2, in Arf6 function

The GTPase-activating protein (GAP) domain for Arfs primarily consists of a zinc-finger structure, which is not present in known GAPs for the other Ras-superfamily GTPases. More than 20 genes have been found to encode proteins bearing the ArfGAP domain in the human genome: a number that is much larger than that of the Arf isoforms. Several Arf isoforms, such as Arf1 and Arf6, indeed have been shown to each employ multiple different ArfGAPs for their regulation and function. We have found that two ArfGAPs, namely AMAP1 and AMAP2, exhibit a novel biochemical property of directly and selectively binding to GTP-Arf6 without immediate GAPing activity, while they were previously shown to exhibit efficient catalytic GAPing activities to Arf isoforms except Arf6 in vitro. Such property of AMAPs appears to be important for AMAPs-mediated recruitment of auxiliary molecules, including paxillin, cortactin, amphiphysin, and intersectin, to sites of Arf6 activation. AMAPs thus appear to act as "effectors" rather than simple GAPs in some aspects of Arf6 function. This article presents methods and protocols developed for the functional characterization of AMAPs in Arf6 function. These methods may be applied to other types of ArfGAPs to further clarify the cellular functions of ArfGAPs as well as Arfs.