Conservation of inter-protein binding sites in RUSH and RFBP, an ATP11B isoform.

Isoforms of RUSH interact with a RING-finger binding protein (RFBP), which is a splice variant of the Type IV P-type ATPase, ATP11B. Splice arrays and RT-PCR showed that although most splice variants in RUSH and ATP11B are conserved in human and rabbit, the RFBP isoform is specific to rabbit. Interactions between the discontinuous PVITHC-HAKCPL sequence in the RING-domain of RUSH and the KVIRLIKIS sequence in the catalytic loop of RFBP were first identified with pull-down assays. Fine mapping involved probing CLIPS-constrained RING peptides with GST-tagged KVIRLIKIS. When the companion site in RFBP was fine mapped by replacement analysis with MBP-tagged RING, a four-fold increase in binding was noted for the KVIRLDKIS mutant. Direct comparison of splicing events in the RUSH and ATP11B genes between human and rabbit shows high structural stability in these protein interactions sites, which are 100% conserved in all mammalian orthologs.