PMID: 30610115 , Related PDB ids: 6B3I, 1A8A, 1W3W
McCulloch KM, Yamakawa I, Shifrin DA Jr, McConnell RE, Foegeding NJ, Singh PK, Mao S, Tyska MJ, Iverson TM
An alternative N-terminal fold of the intestine-specific annexin A13a induces dimerization and regulates membrane-binding.
J Biol Chem. 2019 Mar 8;294(10):3454-3463. doi: 10.1074/jbc.RA118.004571. Epub, 2019 Jan 4.
Annexin proteins function as Ca(2+)-dependent regulators of membrane trafficking and repair that may also modulate membrane curvature. Here, using high-resolution confocal imaging, we report that the intestine-specific annexin A13 (ANX A13) localizes to the tips of intestinal microvilli and determined the crystal structure of the ANX A13a isoform to 2.6 A resolution. The structure revealed that the N terminus exhibits an alternative fold that converts the first two helices and the associated helix-loop-helix motif into a continuous alpha-helix, as stabilized by a domain-swapped dimer. We also found that the dimer is present in solution and partially occludes the membrane-binding surfaces of annexin, suggesting that dimerization may function as a means for regulating membrane binding. Accordingly, as revealed by in vitro binding and cellular localization assays, ANX A13a variants that favor a monomeric state exhibited increased membrane association relative to variants that favor the dimeric form. Together, our findings support a mechanism for how the association of the ANX A13a isoform with the membrane is regulated.